This speeds up the script from about 140ms down to <10ms, even for
changesets that touch a handful of different GML files.
130ms may not feel like much, but it adds up quickly, especially since
we run a dozen scripts during pre-commit.
Now that the GML formatter is both perserving comments and also mostly
agrees to the existing GML style, it can be used to auto-format all the
GML files in the system. This commit does not only contain the scripts
for running the formatting on CI and the pre-commit hook, but also
initially formats all the existing GML files so that the hook is
successfull.
