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_passes/src/lang_items.rs

@@ -155,7 +155,7 @@ impl<'tcx> LanguageItemCollector<'tcx> {
         // have minimum requirements.
 
         if let hir::Node::Item(hir::Item { kind, span: item_span, .. }) =
-            self.tcx.hir().get_by_def_id(item_def_id)
+            self.tcx.hir_node_by_def_id(item_def_id)
         {
             let (actual_num, generics_span) = match kind.generics() {
                 Some(generics) => (