Auto merge of #83188 - petrochenkov:field, r=lcnr

ast/hir: Rename field-related structures

I always forget what `ast::Field` and `ast::StructField` mean despite working with AST for long time, so this PR changes the naming to less confusing and more consistent.

- `StructField` -> `FieldDef` ("field definition")
- `Field` -> `ExprField` ("expression field", not "field expression")
- `FieldPat` -> `PatField` ("pattern field", not "field pattern")

Various visiting and other methods working with the fields are renamed correspondingly too.

The second commit reduces the size of `ExprKind` by boxing fields of `ExprKind::Struct` in preparation for https://github.com/rust-lang/rust/pull/80080.

compiler/rustc_ast_lowering/src/lib.rs

@@ -2559,8 +2559,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         &mut self,
         span: Span,
         pat: &'hir hir::Pat<'hir>,
-    ) -> &'hir [hir::FieldPat<'hir>] {
-        let field = hir::FieldPat {
+    ) -> &'hir [hir::PatField<'hir>] {
+        let field = hir::PatField {
             hir_id: self.next_id(),
             ident: Ident::new(sym::integer(0), span),
             is_shorthand: false,
@@ -2574,7 +2574,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         &mut self,
         span: Span,
         lang_item: hir::LangItem,
-        fields: &'hir [hir::FieldPat<'hir>],
+        fields: &'hir [hir::PatField<'hir>],
     ) -> &'hir hir::Pat<'hir> {
         let qpath = hir::QPath::LangItem(lang_item, span);
         self.pat(span, hir::PatKind::Struct(qpath, fields, false))