Remove double-slashes from Project Paths

[michael-hawker]

Helps with UWP project heads and old-project system now for some reason after single-experiment heads broke with #152 #164

There's still an issue with some projects (like Behaviors) that reference other projects within their source projects (like Animations).

The UWP single-component head isn't picking up that transitive dependency and failing to build. If you manually add the Animations reference to the UWP app head, then it starts working again... Assuming this is some issue with the old-style project, as the WASDK head works fine (before and after this change).

We'll either have to follow-up with the tooling team and/or find a workaround for this in our props files...

[michael-hawker]

Not sure if we'll hit an msbuild issue again in the CI, as we originally had tried to do this when porting Behaviors back here: #20 (comment)

[michael-hawker]

Ugh, same issue as before in previous port of Behaviors project:

2023-08-04T23:24:31.8485112Z        "D:\a\Windows\Windows\CommunityToolkit.AllComponents.sln" (default target) (1:2) ->
2023-08-04T23:24:31.8485695Z        "D:\a\Windows\Windows\tooling\ProjectHeads\AllComponents\Tests.WinAppSdk\CommunityToolkit.Tests.WinAppSdk.csproj" (default target) (51:6) ->
2023-08-04T23:24:31.8486448Z        "D:\a\Windows\Windows\components\Extensions\src\CommunityToolkit.WinUI.Extensions.csproj" (GetTargetPathWithTargetPlatformMoniker target) (15:714) ->
2023-08-04T23:24:31.8487200Z          D:\a\Windows\Windows\components\Extensions\src\CommunityToolkit.WinUI.Extensions.csproj : error MSB4057: The target "GetTargetPathWithTargetPlatformMoniker" does not exist in the project.
2023-08-04T23:24:31.8487584Z 
2023-08-04T23:24:31.8487590Z 
2023-08-04T23:24:31.8487838Z        "D:\a\Windows\Windows\CommunityToolkit.AllComponents.sln" (default target) (1:2) ->
2023-08-04T23:24:31.8488426Z        "D:\a\Windows\Windows\tooling\ProjectHeads\AllComponents\Tests.WinAppSdk\CommunityToolkit.Tests.WinAppSdk.csproj" (default target) (51:6) ->
2023-08-04T23:24:31.8489143Z        "D:\a\Windows\Windows\components\Extensions\src\CommunityToolkit.WinUI.Extensions.csproj" (GetTargetPathWithTargetPlatformMoniker target) (15:715) ->
2023-08-04T23:24:31.8489859Z          D:\a\Windows\Windows\components\Extensions\src\CommunityToolkit.WinUI.Extensions.csproj : error MSB4057: The target "GetTargetPathWithTargetPlatformMoniker" does not exist in the project.
2023-08-04T23:24:31.8490873Z 
2023-08-04T23:24:31.8491219Z     29 Warning(s)
2023-08-04T23:24:31.8493137Z     2 Error(s)

So, we've come around full circle, except this time the double-slashes cause more problems for the Behaviors project...

Not sure if these threads have any info we can use: dotnet/msbuild#8985, dotnet/msbuild#2298, or dotnet/msbuild#4303

[michael-hawker]

Update tooling submodule to main now that tooling pr in.