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`

clippy_lints/src/missing_fields_in_debug.rs

@@ -220,7 +220,7 @@ impl<'tcx> LateLintPass<'tcx> for MissingFieldsInDebug {
             && let self_ty = cx.tcx.type_of(self_path_did).skip_binder().peel_refs()
             && let Some(self_adt) = self_ty.ty_adt_def()
             && let Some(self_def_id) = self_adt.did().as_local()
-            && let Some(Node::Item(self_item)) = cx.tcx.hir().find_by_def_id(self_def_id)
+            && let Some(Node::Item(self_item)) = cx.tcx.opt_hir_node_by_def_id(self_def_id)
             // NB: can't call cx.typeck_results() as we are not in a body
             && let typeck_results = cx.tcx.typeck_body(*body_id)
             && should_lint(cx, typeck_results, block)