… r=Veykril

fix: Don't add reference when it isn't needed for the "Extract variable" assist

I.e. don't generate `let var_name = &foo()`. Because it always irritates me when I need to fix that.

Anything that creates a new value don't need a reference. That excludes mostly field accesses and indexing.

I had a thought that we can also not generate a reference for fields and indexing as long as the type is `Copy`, but sometimes people impl `Copy` even when they don't want to copy the values (e.g. a large type), so I didn't do that.