Rollup merge of #120958 - ShoyuVanilla:remove-subst, r=oli-obk

Dejargonize `subst`

In favor of #110793, replace almost every occurence of `subst` and `substitution` from rustc codes, but they still remains in subtrees under `src/tools/` like clippy and test codes (I'd like to replace them after this)

compiler/rustc_hir/src/hir.rs

@@ -2536,7 +2536,7 @@ pub struct OpaqueTy<'hir> {
     /// lifetimes that are captured from the function signature they originate from.
     ///
     /// This is done by generating a new early-bound lifetime parameter local to the
-    /// opaque which is substituted in the function signature with the late-bound
+    /// opaque which is instantiated in the function signature with the late-bound
     /// lifetime.
     ///
     /// This mapping associated a captured lifetime (first parameter) with the new