Allow prepareRename to return ranges that do not include original position

[mjbvz]

Problem
TypeScript would like to support renaming files by hitting F2 anywhere in the import path.

import * as _ from './dir1/dir2/file'

Here, hitting F2 anywhere in in the string './dir1/dir2/file' should trigger a rename only on the file part of the path. However, in prepareRename, we currently can't return rename ranges that do not include this original rename position. This means that we cannot support hitting F2 anywhere on `'./dir1/dir2/``

Proposal
Relax this restriction, either eliminating it entirely or perhaps only requiring the rename range to be on the same line as the original position

[mjbvz]

We'd also like to support hitting f2 on the class keyword to rename a class:

class Foo {}

This also requires returning a rename range that does not include the original rename position

[jrieken]

@mjbvz I have eased the restrictions and also removed from workaround check from the TS extension but still wasn't able to test this. It seems TS server errors on a rename request on the class-keyword...