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

[Owen Pan via cfe-commits]

owenca wrote:

> This allows git-clang-format to be used on a Windows terminal without manually needing to find the path and invoke the python interpreter. We have a similar script for `scan-build`.

Can you open an issue and link to it from here? It seems `git clang-format` works in Command Prompt without this new batch file.

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