For normal compilation, use .typelib files rather than .gir XML files.
This is much faster.
Rather than using libgirepository, which would try to actually load the
libraries, we use a custom parser.
The language server will still read XML because it needs to access
documentation, which is not in the typelib, but that's generally fine
because it's a long lived process and only has to do that once.
That way, changes to blueprint-regression-tests don't break CI for
unrelated commits (they should instead break the commit that updates
this `git checkout` line).