Rollup merge of #132540 - compiler-errors:gc, r=calebcartwright

Do not format generic consts

We introduced **nightly support** for generic const items in #113522, but formatting of consts was not modified. Making them format *correctly* is hard, so let's just bail formatting them so we don't accidentally strip their generics and where clauses. This is essentially no-op formatting for generic const items.

r? `````@calebcartwright````` or `````@ytmimi`````

compiler/rustc_ast/src/ast.rs

@@ -414,6 +414,12 @@ pub struct WhereClause {
     pub span: Span,
 }
 
+impl WhereClause {
+    pub fn is_empty(&self) -> bool {
+        !self.has_where_token && self.predicates.is_empty()
+    }
+}
+
 impl Default for WhereClause {
     fn default() -> WhereClause {
         WhereClause { has_where_token: false, predicates: ThinVec::new(), span: DUMMY_SP }