Rollup merge of #122780 - GuillaumeGomez:rename-hir-local, r=oli-obk

Rename `hir::Local` into `hir::LetStmt`

Follow-up of #122776.

As discussed on [zulip](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Improve.20naming.20of.20.60ExprKind.3A.3ALet.60.3F).

I made this change into a separate PR because I'm less sure about this change as is. For example, we have `visit_local` and `LocalSource` items. Is it fine to keep these two as is (I supposed it is but I prefer to ask) or not? Having `Node::Local(LetStmt)` makes things more explicit but is it going too far?

r? ```@oli-obk```

Author: matthiaskrgr

compiler/rustc_ast_lowering/src/block.rs

@@ -81,7 +81,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         (self.arena.alloc_from_iter(stmts), expr)
     }
 
-    fn lower_local(&mut self, l: &Local) -> &'hir hir::Local<'hir> {
+    fn lower_local(&mut self, l: &Local) -> &'hir hir::LetStmt<'hir> {
         let ty = l
             .ty
             .as_ref()
@@ -97,7 +97,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let span = self.lower_span(l.span);
         let source = hir::LocalSource::Normal;
         self.lower_attrs(hir_id, &l.attrs);
-        self.arena.alloc(hir::Local { hir_id, ty, pat, init, els, span, source })
+        self.arena.alloc(hir::LetStmt { hir_id, ty, pat, init, els, span, source })
     }
 
     fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {

compiler/rustc_ast_lowering/src/index.rs

@@ -302,8 +302,8 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         });
     }
 
-    fn visit_local(&mut self, l: &'hir Local<'hir>) {
-        self.insert(l.span, l.hir_id, Node::Local(l));
+    fn visit_local(&mut self, l: &'hir LetStmt<'hir>) {
+        self.insert(l.span, l.hir_id, Node::LetStmt(l));
         self.with_parent(l.hir_id, |this| {
             intravisit::walk_local(this, l);
         })