fix: workaround for move to file refactor restriction

[jasonlyu123]

#2222

When using the move to existing file refactor, TypeScript currently throws a Debug.assert error when any file in the program is not a supported file extension. Working around it by monkey patching the program.getSourceFiles method during the getMoveToRefactoringFileSuggestions function call. Let's hope we can convince the TypeScript team to remove this restriction, and we'll no longer need this workaround.

[jasonlyu123]

Find one problem. What if other ts-plugins were returning a new language service and didn't support getProjectVersion? That way, the program object might be updated so that the workaround won't work, and we might also patch the new program with the old getSourceFiles. Might need to find a way to detect that.

[jasonlyu123]

Ok. It shouldn't happen. The getSourceFiles function will only be used to check if existing files are updated. So, fewer files here won't change the up-to-date check results. And the "patch the new program with the old getSourceFile" won't happen either because the new program will be a new object. It won't happen if we patch the one stored in a variable.