Documentation comment code tags do not render as rich text

## Issue Description ##
Some documentation comment tags, namely `code` and `c` do not render rich text and simply display their text contents verbatim as if without the tag.

## Steps to Reproduce ##
Here's an example interface method with all of these:

```
///
/// Begins a transaction on a realm. If a transaction is already in progress for the given realm instance,
/// null is returned, since multiple transactions on a given instance are invalid. This can be used
/// to begin a transaction if not already in one.
///
///
/// using (var transaction = realmService.BeginTransaction())
/// {
/// // do some stuff that needs a write transaction
///
/// // now commit this transaction, or leave the outer transaction to do the committing
/// transaction?.Commit();
/// }
///
///
///
///
/// Note: If a realm is not given, the thread's current instance is used.
///
/// The realm
/// The transaction
Transaction? BeginTransaction(Realm? realm = null);
```

Done [as documented](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/documentation-comments#code)

## Expected Behavior ##
`code` block should be rendered as a code block, and `c` as inline code.

TypeScript docs do this:

## Actual Behavior ##
I get a comment with *some* tags rendering, but not the aforementioned two.

## Logs ##

### OmniSharp log ###

```
Starting OmniSharp server at 7/9/2021, 10:55:17 AM
Target: c:\Users\Matt\Workspace\lab\horizon\project\horizon.sln

OmniSharp server started.
Path: c:\Users\Matt\.vscode\extensions\ms-dotnettools.csharp-1.23.12\.omnisharp\1.37.10\OmniSharp.exe
PID: 19924

[info]: OmniSharp.Stdio.Host
Starting OmniSharp on Windows 6.2.9200.0 (x64)
[info]: OmniSharp.Services.DotNetCliService
DotNetPath set to dotnet
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
Located 3 MSBuild instance(s)
1: Visual Studio Build Tools 2017 15.9.28307.1234 - "C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\MSBuild\15.0\Bin"
2: Visual Studio Community 2019 16.10.31321.278 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"
3: StandAlone 16.11.0 - "c:\Users\Matt\.vscode\extensions\ms-dotnettools.csharp-1.23.12\.omnisharp\1.37.10\.msbuild\Current\Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
Registered MSBuild instance: Visual Studio Community 2019 16.10.31321.278 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"
[info]: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0
[info]: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.Completion.CompletionOptionsProvider, Order: 0
[info]: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.RenameWorkspaceOptionsProvider, Order: 100
[info]: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.ImplementTypeWorkspaceOptionsProvider, Order: 110
[info]: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.BlockStructureWorkspaceOptionsProvider, Order: 140
[info]: OmniSharp.Cake.CakeProjectSystem
Detecting Cake files in 'c:\Users\Matt\Workspace\lab\horizon\project'.
[info]: OmniSharp.Cake.CakeProjectSystem
Could not find any Cake files
[info]: OmniSharp.MSBuild.ProjectSystem
Detecting projects in 'c:\Users\Matt\Workspace\lab\horizon\project\horizon.sln'.
[info]: OmniSharp.MSBuild.ProjectManager
Queue project update for 'c:\Users\Matt\Workspace\lab\horizon\project\packages\engine\horizon-engine.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
Queue project update for 'c:\Users\Matt\Workspace\lab\horizon\project\packages\engine-gen\horizon-engine-generator.csproj'
[info]: OmniSharp.Script.ScriptProjectSystem
Detecting CSX files in 'c:\Users\Matt\Workspace\lab\horizon\project'.
[info]: OmniSharp.MSBuild.ProjectManager
Loading project: c:\Users\Matt\Workspace\lab\horizon\project\packages\engine\horizon-engine.csproj
[info]: OmniSharp.Script.ScriptProjectSystem
Could not find any CSX files
[info]: OmniSharp.WorkspaceInitializer
Configuration finished.
[info]: OmniSharp.Stdio.Host
Omnisharp server running using Stdio at location 'c:\Users\Matt\Workspace\lab\horizon\project' on host 22392.
[info]: OmniSharp.MSBuild.ProjectManager
Successfully loaded project file 'c:\Users\Matt\Workspace\lab\horizon\project\packages\engine\horizon-engine.csproj'.
[info]: OmniSharp.MSBuild.ProjectManager
Adding project 'c:\Users\Matt\Workspace\lab\horizon\project\packages\engine\horizon-engine.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
Loading project: c:\Users\Matt\Workspace\lab\horizon\project\packages\engine-gen\horizon-engine-generator.csproj
[info]: OmniSharp.MSBuild.ProjectManager
Successfully loaded project file 'c:\Users\Matt\Workspace\lab\horizon\project\packages\engine-gen\horizon-engine-generator.csproj'.
[info]: OmniSharp.MSBuild.ProjectManager
Adding project 'c:\Users\Matt\Workspace\lab\horizon\project\packages\engine-gen\horizon-engine-generator.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
Update project: horizon-engine
[info]: OmniSharp.MSBuild.ProjectManager
Update project: horizon-engine-generator
Received response for /completion but could not find request.
Received response for /quickinfo but could not find request.
```

### C# log ###
This is empty.

## Environment information ##

**VSCode version**: 1.58.0
**C# Extension**: 1.23.12

Dotnet Information
.NET SDK (reflecting any global.json):
Version: 5.0.300
Commit: 2e0c8c940e

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19042
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\5.0.300\

Host (useful for support):
Version: 5.0.6
Commit: 478b2f8c0e

.NET SDKs installed:
2.1.801 [C:\Program Files\dotnet\sdk]
2.1.802 [C:\Program Files\dotnet\sdk]
2.2.401 [C:\Program Files\dotnet\sdk]
5.0.300 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET runtimes or SDKs:
https://aka.ms/dotnet-download

Visual Studio Code Extensions

|Extension|Author|Version|
|---|---|---|
|alphabetical-sorter|ue|2.0.1|
|auto-using|Fudge|0.7.15|
|bbcode|rickvansloten|0.0.2|
|change-case|wmaurer|1.0.0|
|cpptools|ms-vscode|1.5.1|
|csharp|ms-dotnettools|1.23.12|
|csharpfixformat|Leopotam|0.0.84|
|debugger-for-chrome|msjsdiag|4.12.12|
|EditorConfig|EditorConfig|0.16.4|
|file-icons|file-icons|1.0.29|
|gitlens|eamodio|11.5.1|
|ilspy-vscode|icsharpcode|0.11.2|
|markdown-all-in-one|yzhang|3.4.0|
|msbuild-project-tools|tintoy|0.3.15|
|msbuild-tools|sterin|0.0.12|
|nord-visual-studio-code|arcticicestudio|0.17.1|
|prettier-vscode|esbenp|8.0.1|
|pug|amandeepmittal|1.0.1|
|python|ms-python|2021.6.944021595|
|remote-wsl|ms-vscode-remote|0.58.2|
|santacodes-region-viewer|SantaCodes|1.0.0|
|sass-lint|glen-84|1.0.7|
|sln-support|logerfo|0.0.1|
|spellright|ban|3.0.58|
|uuid-generator|netcorext|0.0.4|
|vdf|GEEKiDoS|0.0.7|
|vscode-commons|redhat|0.0.6|
|vscode-csproj|lucasazzola|0.7.0|
|vscode-docker|ms-azuretools|1.14.0|
|vscode-dotnet-runtime|ms-dotnettools|1.1.0|
|vscode-eslint|dbaeumer|2.1.23|
|vscode-gitignore-generator|piotrpalarz|1.0.3|
|vscode-nuget-package-manager|jmrog|1.1.6|
|vscode-pylance|ms-python|2021.7.2|
|vscode-solution-explorer|fernandoescolar|0.4.3|
|vscode-xml|redhat|0.17.0|
|vsliveshare|ms-vsliveshare|1.0.4531|
|webgl-glsl-editor|raczzalan|1.2.1|
|xml|DotJoshJohnson|2.5.1|
|yarn-task-provider|dkneeland|0.2.2|;

**Edit:** formatting, typo