Silent glob expansion failure on **.ext

[rainersigwald]

Issue Description

When a recursive-directory glob ** is used directly with an extension, like **.cs instead of **\*.cs, it can silently fail to expand.

Steps to Reproduce

<Project>
  <ItemGroup>
    <I Include="**.proj" />
  </ItemGroup>

  <Target Name="Printer">
    <Message Importance="High" Text="I: @(I)" />
  </Target>
</Project>

In a file named GlobDoesNotExpand.proj

Expected Behavior

❯ msbuild .\GlobDoesNotExpand.proj -v:m
MSBuild version 17.13.0-preview-24563-01+c49eee220 for .NET Framework

  OnlyDirectoryGlob: GlobDoesNotExpand.proj
  DirectoryAndFile: GlobDoesNotExpand.proj

Actual Behavior

❯ msbuild .\GlobDoesNotExpand.proj -v:m
MSBuild version 17.13.0-preview-24563-01+c49eee220 for .NET Framework

  OnlyDirectoryGlob: **.proj
  DirectoryAndFile: GlobDoesNotExpand.proj

Analysis

This can be hard to find because it looks like the C# compiler will accept ..\OtherDirectory\**.cs on the command line and expand it. A Microsoft internal team hit it due to a failure in SourceLink's GetUntrackedFiles task, which didn't expand the glob itself (and shouldn't be expected to IMO).

Versions & Configurations

No response