Rollup merge of #34355 - jseyfried:paren_expression_ids_nonunique, r=nrc

Give `ast::ExprKind::Paren` no-op expressions the same ids as their children.

Having `ast::ExprKind::Paren` expressions share ids with their children
 - reduces the number of unused `NodeId`s in the hir map and
 - guarantees that `tcx.map.expect_expr(ast_expr.id)` is the hir corresponding to `ast_expr`.

This fixes the bug from #34327, which was introduced in #33296 when I assumed the above guarantee.

r? @nrc