Missing XML comments from Base Classes / Interfaces using Inheritdoc

## Issue Description ##
`` does not show documentation from base classes / interfaces when using Intellisense. This includes:
- when hovering with the mouse
- when using regular intellisense
- when manually resolving the inheritence using `cref`.

#3652 fixed `` within the same class, but the functionality is still missing when using `` for methods/properties defined in base classes / interfaces.

This issue makes the developer experience in VSCode more difficult since it makes it harder to share XML docs and requires the developer to go to base classes / directly to view the XML docs. Since VS2019 has the functionality I expect, it makes me want to do development in VS2019 instead of VSCode when working in C#.

## Steps to Reproduce ##
1. Create a base class / interface that has XML docs in it (or use one from any standard library like Attribute.)
2. Create a class that inherits / implements from the base class / interface
3. Override / implement a method / property on the base class / interface.
4. Mark the method / property with ``
5. Notice that no intellisense shows up for the derived method/property.
6. Add `cref=.Post the output from Output-->OmniSharp log here

### C# log ###
Installing C# dependencies...
Platform: linux, x86_64, name=ubuntu, version=20.04

Downloading package 'OmniSharp for Linux (x64)' (36731 KB).................... Done!
Validating download...
Integrity Check succeeded.
Installing package 'OmniSharp for Linux (x64)'

Downloading package '.NET Core Debugger (linux / x64)' (59506 KB).................... Done!
Validating download...
Integrity Check succeeded.
Installing package '.NET Core Debugger (linux / x64)'

Downloading package 'Razor Language Server (Linux / x64)' (61682 KB).................... Done!
Installing package 'Razor Language Server (Linux / x64)'

Finished

## Environment information ##

**VSCode version**: 1.59.1
**C# Extension**: 1.23.14

Mono Information
OmniSharp using built-in mono
Dotnet Information
.NET SDK (reflecting any global.json):
Version: 5.0.302
Commit: c005824e35

Runtime Environment:
OS Name: ubuntu
OS Version: 20.04
OS Platform: Linux
RID: ubuntu.20.04-x64
Base Path: /usr/share/dotnet/sdk/5.0.302/

Host (useful for support):
Version: 5.0.8
Commit: 35964c9215

.NET SDKs installed:
5.0.302 [/usr/share/dotnet/sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 5.0.8 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 5.0.8 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

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

Visual Studio Code Extensions

|Extension|Author|Version|
|---|---|---|
|code-spell-checker|streetsidesoftware|1.10.2|
|csharp|ms-dotnettools|1.23.14|
|EditorConfig|EditorConfig|0.16.4|
|githistory|donjayamanne|0.6.18|
|gitlens|eamodio|11.6.0|
|output-colorizer|IBM|0.1.2|
|terraform|hashicorp|2.14.0|
|todo-tree|Gruntfuggly|0.0.213|
|vscode-docker|ms-azuretools|1.16.0|
|vscode-markdownlint|DavidAnson|0.43.2|
|vscode-proto3|zxh404|0.5.4|
|vscode-yaml|redhat|0.22.0|;