[clang] [Windows] Add git-clang-format wrapper bat file (PR #69228)

[Chris B via cfe-commits]

llvm-beanz wrote:

> Can you open an issue and link to it from here?

Filed #69643.

> It seems `git clang-format` works in Command Prompt without this new batch file.

IIUC, `git clang-format` works if you have WSL installed, but not with a default Windows installation. We definitely have users on my team that are Windows-only users who encounter an error running that command even if the git-clang-format script is on the path, and the presence of the `.bat` file solves the issue.

https://github.com/llvm/llvm-project/pull/69228