project: centralize safe branch and commit resolution

Resolve commit-ish values through one typed helper using rev-parse
--verify --quiet and, on Git 2.30+, --end-of-options. Reject option-like
revisions on older clients, reuse the helper for project and manifest
resolution, and validate user branch names with check-ref-format
--branch.

Bug: 553599402
Change-Id: I2dda49ff3e781cec14d3b84263a8dace06b4073f
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/623182
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Brian Gan <brgan@google.com>

git_command.py

@@ -70,6 +70,19 @@ class _GitCall:
 git = _GitCall()
 
 
+def IsValidBranchName(name: str) -> bool:
+    """Return whether |name| is valid where Git expects a branch name."""
+    p = GitCommand(
+        None,
+        ["check-ref-format", "--branch", name],
+        capture_stdout=True,
+        capture_stderr=True,
+        add_event_log=False,
+        log_as_error=False,
+    )
+    return p.Wait() == 0
+
+
 def RepoSourceVersion():
     """Return the version of the repo.git tree."""
     ver = getattr(RepoSourceVersion, "version", None)