* Fix path data in FrameworkList.xml
* Move FrameworkList.xml to SharedFxRoot
* Fix targeting pack xml test
* Add test
* Add another test
* Extract .xml files to Helix as well
* Add another test
* Update TestRunner.cs
* Remove slash
- correct Helix test failures with stable versions, where SDK's packs aren't enough
E.g. from https://dev.azure.com/dnceng/internal/_build/results?buildId=813814
``` text
...\.dotnet\sdk\5.0.100-rc.1.20379.10\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.FrameworkReferenceResolution.targets(318,5): error MSB4018: The "ResolveTargetingPackAssets" task failed unexpectedly. [...\src\ProjectTemplates\test\bin\Release\net5.0\TestTemplates\AspNet.m0yq3xrporu\AspNet.m0yq3xrporu.csproj]
...\.dotnet\sdk\5.0.100-rc.1.20379.10\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.FrameworkReferenceResolution.targets(318,5): error MSB4018: System.IO.DirectoryNotFoundException: Could not find a part of the path '...\.dotnet\packs\Microsoft.AspNetCore.App.Ref\5.0.0\data\FrameworkList.xml'. [...\src\ProjectTemplates\test\bin\Release\net5.0\TestTemplates\AspNet.m0yq3xrporu\AspNet.m0yq3xrporu.csproj]
```
* Eliminate duplicates in Helix `TestRunner`
- do not add source that's already in NuGet.config
- configuration file now part of Helix content
- do not re-set an env variable that's set in `runtests.*`
nit: simplify `%Path% setting in runtests.cmd
- always quote the value
- but, keep the `SETLOCAL` command
- don't pollute environment on Helix agents
* Remove `--source` options we don't need anymore from `runtests.*`
- nit: add `--no-restore` to `dotnet run` command after `dotnet restore`
* Add `--arch arm64` to ARM64 `restore` build steps
- #25397
- was restoring for the wrong architecture
nit: add `--no-restore` to Helix project build steps
- already restored
* Remove extra `[SkipOnHelix]` attribute
- only need the one compiled into Microsoft.AspNetCore.Testing
- update the documentation to reflect this
- nit: address Markdown warnings that VS Code showed
* Add `SuccessfulTests` to ensure something runs in every non-Helix runs
- #22241
- cleans up hundreds of warnings but leaves a couple for the Blazor tests assembly
- see comments about xUnit runner command line in the new class
William Godbe
Doug Bunting
Hao Kung
Brennan