Move pre-mount validation from gvfs.exe to gvfs.mount.exe

Move authentication, server config query, version validation, cache
health checks, git config settings, and enlistment logging from the
mount verb (gvfs.exe) into the mount process (gvfs.mount.exe). This
eliminates duplicate work (auth and index parsing were done in both
processes) and reduces mount time from ~40s to ~22s.

The verb now only does: disk layout upgrade check, ProjFS attach,
enum arg validation, mount exe existence check, launch + wait.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: tyrielv