Move MirPatch from rustc_middle to rustc_mir_transform.

Because it's only used in `rustc_mir_transform`. (Presumably it is
currently in `rustc_middle` because lots of other MIR-related stuff is,
but that's not a hard requirement.) And because `rustc_middle` is huge
and it's always good to make it smaller.

compiler/rustc_mir_transform/src/shim.rs

@@ -6,7 +6,6 @@ use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_index::{Idx, IndexVec};
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::*;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::adjustment::PointerCoercion;
@@ -19,6 +18,7 @@ use rustc_span::{DUMMY_SP, Span};
 use tracing::{debug, instrument};
 
 use crate::elaborate_drop::{DropElaborator, DropFlagMode, DropStyle, Unwind, elaborate_drop};
+use crate::patch::MirPatch;
 use crate::{
     abort_unwinding_calls, add_call_guards, add_moves_for_packed_drops, deref_separator, inline,
     instsimplify, mentioned_items, pass_manager as pm, remove_noop_landing_pads, simplify,