When globbing returns original filespec

Original itemspec is returned when:

• illegal filespec contains
  • both wildcards and escaped wildcards (%2a, %3f)
  • illegal file chars
  • ...
  • a : anywhere but the second character
  • a .. after a wildcard
  • a path fragment which contains ** and other characters (e.g. /**f/)
• Any IO related exception is thrown during file walking: https://github.com/dotnet/msbuild/blob/c1d949558b4808ca9381d09af384b66b31cde2b2/src/Shared/ExceptionHandling.cs#L125-L140
  • System.UnauthorizedAccessException and System.Security.SecurityException from directory enumeration (Directory.EnumerateFileSystemEntries) are ignored, and the files / directories which cause it are excluded from the results.