#39661 [Dridi's PATCH 4/9] Replace PostBuildEvent scripts with XML targets

#39661 [Dridi's PATCH 4/9] Replace PostBuildEvent scripts with XML targets
This becomes portable outside the usual build environment. In particular it becomes possible to build on GNU/Linux (instead of Windows) for Mono (instead of .NET) with xbuild (instead of msbuild).
Instead of preserving "newer" files during the copy, it is now done on a systematic way to keep the tasks simple. This shouldn't be a problem for the low volume of files that get copied during a build.
Also, some of the copying is hard to reproduce with the Copy command so some of it is omitted with this change.