Bazel: introduce buildifier formatting

This introduces tooling and enforcement for formatting bazel files.

The tooling is provided as a bazel run target from
[keith/buildifier-prebuilt](https://github.com/keith/buildifier-prebuilt).

This is used in a [`pre-commit`](https://pre-commit.com/) hook for those
having that installed. In turn this is used in a CI check. Relying on a
`pre-commit` action gives us easy checking that buildifying did not
change anything in the files and printing the diff, without having to
hand-roll the check ourselves.

This enforcement will make usage of gazelle easier, as gazelle itself
might reformat files, even outside of `go`. Having them properly
formatted will allow gazelle to leave them unchanged, without needing
to configure awkward exclude directives.

python/extractor/tsg-python/tsp/BUILD.bazel

@@ -1,6 +1,6 @@
+load("@py_deps//:defs.bzl", "aliases", "all_crate_deps")
 load("@rules_rust//cargo:defs.bzl", "cargo_build_script")
 load("@rules_rust//rust:defs.bzl", "rust_library")
-load("@py_deps//:defs.bzl", "aliases", "all_crate_deps")
 
 package(default_visibility = ["//visibility:public"])