Should not allow renaming keywords

[mjbvz]

TS-go will allow triggering rename anywhere in the file, including on parens and keywords. When you press enter it will then either try doing a rename or say no result

Instead we should fail the rename early. Here's what happens in TS 6

I believe this warning comes from the prepareRename call

[mjbvz]

In 6.0 we do allow triggering renames on class and similar keywords but this shifts the rename to the class name instead