rustc_interface: Address all rustc::potential_query_instability lints

Instead of allowing `rustc::potential_query_instability` on the whole
crate we go over each lint and allow it individually if it is safe to
do. Turns out all instances were safe to allow in this crate.

compiler/rustc_interface/src/lib.rs

@@ -6,7 +6,6 @@
 #![feature(let_chains)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
-#![allow(rustc::potential_query_instability)]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]