Replace the QueryEngine with Salsa

[JoshuaBatty]

Salsa is a lot more sophisticated than the QueryEngine that we rely on. It could be a good first step to replace the existing query engine with Salsa. After this step is done, it should unlock progress for more granular caching at the AstNode level.

One of the reasons the QueryEngine was made in the first place was due to salsa being old and not maintained. This seems to have changed in the past 2 months and there is now a big push to stabilise and get a version 3.0 released. Once this is ready it could be a good time to investigate this.