ASP.NET Core Tag helpers intellisense not working

## Issue Description ##
Whenever I am using ASP.NET Core Tag helpers in .cshtml file the intellisense is not working.

## Steps to Reproduce ##
create an input field. and try to type 'asp' attribute and press ctr+space.

## Expected Behavior ##
it should show some tooltip

## Actual Behavior ##

## Logs ##

### OmniSharp log ###

Starting OmniSharp server at 6/15/2021, 12:45:04 PM
Target: c:\Users\DELL\Desktop\MathAnswers\MathAnswers.sln

OmniSharp server started.
Path: c:\Users\DELL\.vscode\extensions\ms-dotnettools.csharp-1.23.12\.omnisharp\1.37.10\OmniSharp.exe
PID: 13768

[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 Community 2019 16.9.31129.286 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"
2: StandAlone 16.11.0 - "c:\Users\DELL\.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 16.9.31129.286 - "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\DELL\Desktop\MathAnswers'.
[info]: OmniSharp.Cake.CakeProjectSystem
Could not find any Cake files
[info]: OmniSharp.MSBuild.ProjectSystem
Detecting projects in 'c:\Users\DELL\Desktop\MathAnswers\MathAnswers.sln'.
[info]: OmniSharp.MSBuild.ProjectManager
Queue project update for 'c:\Users\DELL\Desktop\MathAnswers\MathAnswers\MathAnswers.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
Queue project update for 'c:\Users\DELL\Desktop\MathAnswers\Tests\Tests.csproj'
[info]: OmniSharp.Script.ScriptProjectSystem
Detecting CSX files in 'c:\Users\DELL\Desktop\MathAnswers'.
[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\DELL\Desktop\MathAnswers' on host 3680.
[info]: OmniSharp.MSBuild.ProjectManager
Loading project: c:\Users\DELL\Desktop\MathAnswers\MathAnswers\MathAnswers.csproj
[info]: OmniSharp.MSBuild.ProjectManager
Successfully loaded project file 'c:\Users\DELL\Desktop\MathAnswers\MathAnswers\MathAnswers.csproj'.
[info]: OmniSharp.MSBuild.ProjectManager
Adding project 'c:\Users\DELL\Desktop\MathAnswers\MathAnswers\MathAnswers.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
Loading project: c:\Users\DELL\Desktop\MathAnswers\Tests\Tests.csproj
[info]: OmniSharp.MSBuild.ProjectManager
Successfully loaded project file 'c:\Users\DELL\Desktop\MathAnswers\Tests\Tests.csproj'.
[info]: OmniSharp.MSBuild.ProjectManager
Adding project 'c:\Users\DELL\Desktop\MathAnswers\Tests\Tests.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
Update project: MathAnswers
[info]: OmniSharp.MSBuild.ProjectManager
Update project: Tests

### C# log ###
No logs

## Environment information ##

**VSCode version**: 1.57.0
**C# Extension**: 1.23.12

Dotnet Information
.NET SDK (reflecting any global.json):
Version: 5.0.201
Commit: a09bd5c86c

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19042
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\5.0.201\

Host (useful for support):
Version: 5.0.4
Commit: f27d337295

.NET SDKs installed:
3.1.404 [C:\Program Files\dotnet\sdk]
5.0.101 [C:\Program Files\dotnet\sdk]
5.0.201 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.26 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.26 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.26 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.10 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.13 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.4 [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|
|---|---|---|
|auto-rename-tag|formulahendry|0.1.6|
|bracket-pair-colorizer-2|CoenraadS|0.2.1|
|cpptools|ms-vscode|1.4.1|
|csharp|ms-dotnettools|1.23.12|
|debugger-for-chrome|msjsdiag|4.12.12|
|es7-react-js-snippets|dsznajder|3.1.1|
|go|golang|0.25.1|
|jupyter|ms-toolsai|2021.6.999230701|
|latex-workshop|James-Yu|8.19.2|
|LiveServer|ritwickdey|5.6.1|
|material-theme|zhuangtongfa|3.10.14|
|python|ms-python|2021.5.926500501|
|remote-wsl|ms-vscode-remote|0.56.5|
|vsc-community-material-theme|Equinusocio|1.4.2|
|vscode-commons|redhat|0.0.6|
|vscode-docker|ms-azuretools|1.13.0|
|vscode-eslint|dbaeumer|2.1.22|
|vscode-firefox-debug|firefox-devtools|2.9.4|
|vscode-icons|vscode-icons-team|11.5.0|
|vscode-pylance|ms-python|2021.6.1|
|vscode-sqlite|alexcvzz|0.13.0|
|vscode-tailwindcss|bradlc|0.6.9|
|vscode-xml|redhat|0.16.1|;