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/unnecessary_struct_initialization.rs

@@ -82,7 +82,7 @@ impl LateLintPass<'_> for UnnecessaryStruct {
 
 fn is_mutable(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     if let Some(hir_id) = path_to_local(expr)
-        && let Node::Pat(pat) = cx.tcx.hir().get(hir_id)
+        && let Node::Pat(pat) = cx.tcx.hir_node(hir_id)
     {
         matches!(pat.kind, PatKind::Binding(BindingAnnotation::MUT, ..))
     } else {