manifest: validate project name & path and include name attributes

These attribute values are used to construct local filesystem paths,
so apply the existing filesystem checks to them.

Bug: https://crbug.com/gerrit/14156
Change-Id: Ibcceecd60fa74f0eb97cd9ed1a9792e139534ed4
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/298443


Reviewed-by: Michael Mortensen <mmortensen@google.com>
Tested-by: Mike Frysinger <vapier@google.com>