Fix accidently quadratic syntax rewriter
Fix accidently quadratic syntax rewriter

Switching from SyntaxNode to GreenNode is a costly operation (b/c
dereferencing a synax ptr in `with_green` is linear), so we should
avoid that.

rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer