Integrate Razor VSCode extension functional tests into src/Razor.

- Added the `.vscode-test` to `.gitignore` because that's the VSCode folder that gets created when dynamically downloading VSCode for CI purposes.
- Migrated functional tests to use the non-deprecated VSCode functional testing APIs. This involved creating a runTest file to control downloading VSCode and passing in appropriate parameters as well as creating an index that discovers tests that should be run.
- Changed functional tests to operate on the existing Razor testapps (instead of the old ones).
- Updated the "default" completion tests to be latest Razor/Blazor.
- Added VSCode launch configurations to enable easy debugging via F5.

aspnet/AspNetCoredotnet/aspnetcore-tooling#13494
\n\nCommit migrated from 66e4e8a169

src/Razor/test/testassets/MvcWithComponents/Views/_ViewImports.cshtml

@@ -1,3 +1,4 @@
 @using MvcWithComponents
 @using MvcWithComponents.Models
 @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
+@inject DateTime TheTime

src/Razor/test/testassets/SimpleMvc/Views/_ViewImports.cshtml

@@ -1,3 +1,4 @@
 @using SimpleMvc
 @using SimpleMvc.Models
 @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
+@inject DateTime TheTime

src/Razor/test/testassets/SimpleMvc11/Views/_ViewImports.cshtml

@@ -1,2 +1,3 @@
 @using SimpleMvc11
 @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
+@inject DateTime TheTime

src/Razor/test/testassets/SimpleMvc21/Views/_ViewImports.cshtml

@@ -2,3 +2,4 @@
 @using SimpleMvc.Models
 @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
 @namespace SimpleMvc21
+@inject DateTime TheTime

src/Razor/test/testassets/SimpleMvc22/Views/_ViewImports.cshtml

@@ -2,3 +2,4 @@
 @using SimpleMvc.Models
 @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
 @namespace SimpleMvc21
+@inject DateTime TheTime