This adds these things:
- Buildsystem-Plumbing for allowing more indenters
- An option for using it in test-widget (Albeit I can reverse this one easily)
- Indenter for Vala
- A few unit tests for the indenter (Implemented a bit hacky, as I didn't find a way that does not involve dozens of files)
This MR is a draft because of these issues:
- A lot of unnecessary allocations+a bit of codestyle probably
- Maybe a few missing unit tests
Would resolve gnome-builder#1662 as the pipeline-addin is already ported.
(I will remove the changes to the test-widget as soon as it is ready to land)