Add -MapDriveForShorterPaths option
This adds a -MapDriveForShorterPaths option which maps the working directory to a drive to run the build with shorter paths.
Also:
- Updates the generate plugin/project scripts to use the new build graph generation, and removes the old Generate_ConvertBuildGraphToGitLab.ps1 script.
- Fixed an issue where -WindowsLinuxToolchainPath was unexpectedly mandatory for engines and plugins.