Auto merge of #86251 - Smittyvb:thir-tree-again, r=oli-obk

Support -Z unpretty=thir-tree again

Currently `-Z unpretty=thir-tree` is broken after some THIR refactorings. This re-implements it, making it easier to debug THIR-related issues.

We have to do analyzes before getting the THIR, since trying to create THIR from invalid HIR can ICE. But doing those analyzes requires the THIR to be built and stolen. We work around this by creating a separate query to construct the THIR tree string representation.

Closes https://github.com/rust-lang/project-thir-unsafeck/issues/8, fixes #85552.