Update revisionId if required when using extend-project

When a hard revision ID is provided in a regular project tag then the
revisionId is updated as well if it is a commit hash.  The difference
is that if the revisionExpr is a commit, git-repo needs to update
refs/remotes/m/master with update-ref not symbolic-ref, as the latter
must refer to another ref, not to a specific commit.

Change-Id: I215a62dabb30225e480ad2c731416d775fc0c750
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/310963
Tested-by: Michael Kelly <mkelly@arista.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

manifest_xml.py

@@ -887,13 +887,11 @@ https://gerrit.googlesource.com/git-repo/+/HEAD/docs/manifest-format.md
           if groups:
             p.groups.extend(groups)
           if revision:
-            p.revisionExpr = revision
-            if IsId(revision):
-              p.revisionId = revision
-            else:
-              p.revisionId = None
+            p.SetRevision(revision)
+
           if remote:
             p.remote = remote.ToRemoteSpec(name)
+
           if dest_path:
             del self._paths[p.relpath]
             relpath, worktree, gitdir, objdir, _ = self.GetProjectPaths(name, dest_path)