Revert "Rollup merge of #87779 - Aaron1011:stmt-ast-id, r=petrochenkov"

Fixes #87877

This change interacts badly with `noop_flat_map_stmt`,
which synthesizes multiple statements with the same `NodeId`.

I'm working on a better fix that will still allow us to
remove this special case. For now, let's revert the change
to fix the ICE.

This reverts commit a4262cc984, reversing
changes made to 8ee962f88e.

compiler/rustc_expand/src/expand.rs

@@ -559,7 +559,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         self.cx.force_mode = orig_force_mode;
 
         // Finally incorporate all the expanded macros into the input AST fragment.
-        let mut placeholder_expander = PlaceholderExpander::default();
+        let mut placeholder_expander = PlaceholderExpander::new(self.cx, self.monotonic);
         while let Some(expanded_fragments) = expanded_fragments.pop() {
             for (expn_id, expanded_fragment) in expanded_fragments.into_iter().rev() {
                 placeholder_expander
@@ -1341,9 +1341,14 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
             }
         }
 
+        // The placeholder expander gives ids to statements, so we avoid folding the id here.
         // We don't use `assign_id!` - it will be called when we visit statement's contents
         // (e.g. an expression, item, or local)
-        let res = noop_flat_map_stmt(stmt, self);
+        let ast::Stmt { id, kind, span } = stmt;
+        let res = noop_flat_map_stmt_kind(kind, self)
+            .into_iter()
+            .map(|kind| ast::Stmt { id, kind, span })
+            .collect();
 
         self.cx.current_expansion.is_trailing_mac = false;
         res