Auto merge of #118375 - ouz-a:add_emit_stable_mir_tests, r=celinval

Add -Zunpretty=stable-mir output test

As strongly suggested here rust-lang/rust#118364 (comment) this adds output test for `-Zunpretty=stable-mir`, added test shows almost all the functionality of the current printer.

r? `@compiler-errors`

Author: bors