Blazor WASM - Invalid Intellisense Warnings/Errors

## Issue Description ##
Invalid Intellisense warnings/errors in a brand new Blazor WASM project. In particular, it doesn't recognize the `App` type in `Program.cs` and it doesn't recognize the components in `App.razor`. In practice, however, the application compiles and runs perfectly.

## Steps to Reproduce ##

* Create a new Blazor WASM project (in my case, a PWA): `dotnet new blazorwasm -o project --pwa`
* Open the project in VS Code: `code .\project`
* Review the Intellisense in `Program.cs`, `App.razor`, and `_Imports.razor`.

## Expected Behavior ##

I'd expect a brand new project to show no errors.

## Actual Behavior ##

Intellisense shows invalid warnings and errors and the OmniSharp log shows the same error.



## Logs ##

### OmniSharp log ###

Starting OmniSharp server at 6/30/2021, 7:57:05 PM
Target: c:\Users\Tanner\code\blazor-sample

OmniSharp server started.
Path: c:\Users\Tanner\.vscode\extensions\ms-dotnettools.csharp-1.23.12\.omnisharp\1.37.10\OmniSharp.exe
PID: 8408

[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 2 MSBuild instance(s)
1: Visual Studio Professional 2019 16.9.31205.134 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Current\Bin"
2: StandAlone 16.11.0 - "c:\Users\Tanner\.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 Professional 2019 16.9.31205.134 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\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\Tanner\code\blazor-sample'.
[info]: OmniSharp.Cake.CakeProjectSystem
Could not find any Cake files
[info]: OmniSharp.MSBuild.ProjectSystem
No solution files found in 'c:\Users\Tanner\code\blazor-sample'
[info]: OmniSharp.MSBuild.ProjectManager
Queue project update for 'c:\Users\Tanner\code\blazor-sample\blazor-sample.csproj'
[info]: OmniSharp.Script.ScriptProjectSystem
Detecting CSX files in 'c:\Users\Tanner\code\blazor-sample'.
[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\Tanner\code\blazor-sample' on host 21248.
[info]: OmniSharp.MSBuild.ProjectManager
Loading project: c:\Users\Tanner\code\blazor-sample\blazor-sample.csproj
[info]: OmniSharp.MSBuild.ProjectManager
Successfully loaded project file 'c:\Users\Tanner\code\blazor-sample\blazor-sample.csproj'.
[info]: OmniSharp.MSBuild.ProjectManager
Adding project 'c:\Users\Tanner\code\blazor-sample\blazor-sample.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
Update project: blazor-sample
[info]: OmniSharp.Roslyn.CSharp.Services.Diagnostics.CSharpDiagnosticWorkerWithAnalyzers
Solution initialized -> queue all documents for code analysis. Initial document count: 3.
Received response for /v2/getcodeactions but could not find request.
Received response for /quickinfo but could not find request.

### C# log ###
None

## Environment information ##

**VSCode version**: 1.57.1
**C# Extension**: 1.23.12

Dotnet Information
.NET SDK (reflecting any global.json):
Version: 5.0.202
Commit: db7cc87d51

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19043
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\5.0.202\

Host (useful for support):
Version: 5.0.5
Commit: 2f740adc14

.NET SDKs installed:
5.0.202 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.27 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.27 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.27 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.13 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.14 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.5 [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|
|---|---|---|
|blazorwasm-companion|ms-dotnettools|1.1.0|
|csharp|ms-dotnettools|1.23.12|
|csharpextensions|jchannon|1.3.1|
|powershell|ms-vscode|2021.6.2|
|prettify-json|mohsen1|0.0.3|
|remote-containers|ms-vscode-remote|0.183.0|
|remote-wsl|ms-vscode-remote|0.56.5|
|TabOut|albert|0.2.0|
|vscode-docker|ms-azuretools|1.14.0|
|vscode-dotnet-runtime|ms-dotnettools|1.1.0|
|vscode-icons|vscode-icons-team|11.5.0|
|vscodeintellicode|VisualStudioExptTeam|1.2.14|;

Reproduce the report with `dotnet new blazorwasm -o project --pwa`, open it in VS Code, and inspect `Program.cs`, `App.razor`, and `_Imports.razor` alongside the OmniSharp log. Compare the diagnostics with the successful build and use the supplied VS Code, C# extension, and .NET SDK versions. Done means a new project shows no invalid IntelliSense warnings or errors.

Rédigé par le modèle d'indexation à partir du texte de l'issue.