[scss] rename not working for placeholder selectors

<!-- Please search existing issues to avoid creating duplicates. --> <!-- Also please test using the latest insiders build to make sure your issue has not already been fixed: https://code.visualstudio.com/insiders/ --> <!-- Use Help > Report Issue to prefill these. --> - VSCode Version: 1.28.2 - OS Version: Windows 10 ## Note: this only happens for `.scss` file types, as `.sass` is not supported by VSCode without extensions. Steps to Reproduce: 1. Place cursor over sass placeholder selector 2. Initiate "Rename Symbol" command (through command palette, keyboard shortcuts, etc.) 3. Attempt to rename After completion, the text editor will have renamed the variable throughout the document but removed the leading percent sign in the process. Even this can be dealt with by including a leading percent sign while renaming, it should be considered an issue because when the user does not take the effort to work around this quirk, the behavior of the selector is changed. Example: ```sass %foo { ... } .bar { @extends %foo; } ``` Attempting to rename `foo` to `foobar` results with this: ```sass foobar { ... } .bar { @extends foobar; } ``` Rather than expected: ```sass %foobar { ... } .bar { @extends %foobar; } ``` Does this issue occur when all extensions are disabled?: Yes