Rollup merge of #107006 - b-naber:thir-tree, r=jackh726

Output tree representation on thir-tree

The current output of `-Zunpretty=thir-tree` is really cumbersome to work with, using an actual tree representation should make it easier to see what the thir looks like.

diff --cc compiler/rustc_driver/src/pretty.rs
Simple merge

diff --cc compiler/rustc_middle/src/query/mod.rs
Simple merge

diff --cc compiler/rustc_mir_build/src/build/mod.rs
Simple merge

diff --cc compiler/rustc_session/src/config.rs
Simple merge