Auto merge of #108493 - cjgillot:thir-print, r=compiler-errors

Move THIR printing to rustc_mir_build.

rust-lang/rust#107451 increased the compilation time of `rustc_middle` by 10% = 3s.

As rust-lang/rust#107006 adds quite a lot of code to rustc_middle, I suspect it to be the cause.

This PR moves the THIR printing code to `rustc_mir_build`, where the query provider lives, in order to benefit from higher parallelism when compiling rustc.

Author: bors