Make sure that *.* always means all files in FileMatcher

[ladipro]

Context

#6151 introduced a regression where FileMatcher takes the pattern *.* too literally and returns only files that have a dot in the name. *.* should be special cased to mean all files in the directory, with or without an extension.

Changes Made

Fixed the regression by explicitly testing for *.* and added test coverage.

Testing

Existing and modified unit tests, repro project from dotnet/sdk#16185 (comment).

Notes

Testing for both * and *.* is already happening elsewhere in the class. MSBuild calls Directory.EnumerateFileSystemEntries which under the covers uses MatchType.Win32 and causes this behavior of unifying *.* with * on all platforms.

[benvillalobos]

(copy/pasting my comment from teams here)
For the same reason as #6234 (review) we should have a test that explicitly covers this scenario

[ladipro]

This PR includes test changes that cover the scenario. I.e. the updated tests would fail if the regression is re-introduced.