Move some methods from tcx.hir() to tcx

Renamings:
- find -> opt_hir_node
- get -> hir_node
- find_by_def_id -> opt_hir_node_by_def_id
- get_by_def_id -> hir_node_by_def_id

Fix rebase changes using removed methods

Use `tcx.hir_node_by_def_id()` whenever possible in compiler

Fix clippy errors

Fix compiler

Apply suggestions from code review

Co-authored-by: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>

Add FIXME for `tcx.hir()` returned type about its removal

Simplify with with `tcx.hir_node_by_def_id`

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -50,7 +50,7 @@ impl<'tcx> MirPass<'tcx> for InstrumentCoverage {
         }
 
         let is_fn_like =
-            tcx.hir().get_by_def_id(mir_source.def_id().expect_local()).fn_kind().is_some();
+            tcx.hir_node_by_def_id(mir_source.def_id().expect_local()).fn_kind().is_some();
 
         // Only instrument functions, methods, and closures (not constants since they are evaluated
         // at compile time by Miri).