This patch adds the file provider which is responsible for capturing files used by LLDB.
When capturing a reproducer, we use a file collector that is very similar to the one used in clang. For every file that we touch, we add an entry with a mapping from its virtual to its real path. When we decide to generate a reproducer we copy over the files and their permission into to reproducer folder.
When replaying a reproducer, we load the VFS mapping and instantiate a `RedirectingFileSystem`. The latter will transparently use the files available in the reproducer.
I've tested this on two macOS machines with an artificial example. Still, it is very likely that I missed some places where we (still) use native file system calls. I'm hoping to flesh those out while testing with more advanced examples. However, I will fix those things in separate patches.