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_incremental/src/persist/dirty_clean.rs

@@ -232,7 +232,7 @@ impl<'tcx> DirtyCleanVisitor<'tcx> {
     /// Return all DepNode labels that should be asserted for this item.
     /// index=0 is the "name" used for error messages
     fn auto_labels(&mut self, item_id: LocalDefId, attr: &Attribute) -> (&'static str, Labels) {
-        let node = self.tcx.hir().get_by_def_id(item_id);
+        let node = self.tcx.hir_node_by_def_id(item_id);
         let (name, labels) = match node {
             HirNode::Item(item) => {
                 match item.kind {