Replace hand-written pre-commit hooks with `pre-commit` Python tool

`pre-commit` can be installed with pip, and configured in the Godot repo with
`pre-commit install`. It can then easily be run both locally with
`pre-commit run`, and on CI, in a cross-platform way.

This makes it much easier for contributors to set up pre-commit hooks,
without having to manually copy files to their git folder.

Co-authored-by: Rémi Verschelde <[email protected]>