[semantic highlighting] Source language suffix should be added to semantic token fallback scopes when looked up

Version: 1.58.0 (user setup) Commit: 2d23c42a936db1c7b3b06f918cde29561cc47cd6 Date: 2021-07-08T06:54:55.083Z Electron: 12.0.13 Chrome: 89.0.4389.128 Node.js: 14.16.0 V8: 8.9.255.25-electron.0 OS: Windows_NT x64 10.0.19043 This is based on the following issue reported against the C/C++ Extension: https://github.com/microsoft/vscode-cpptools/issues/7773 Themes can provide colorization specific to a language, using the language ID as a suffix on the TextMate scope. (i.e. `storage.type.cs` or `variable.language.wildcard.java` - examples taken from default themes). However, when VS Code looks up [fallback TextMate scopes for semantic tokens](https://code.visualstudio.com/api/language-extensions/semantic-highlight-guide#semantic-token-scope-map), it does not appear to append the language ID to that scope. Providing separate scopes for each language ID supported by the C/C++ Extension (including for all default fallback scopes) in our `package.json`, appears to work around the issue (an example in [this comment](https://github.com/microsoft/vscode-cpptools/issues/7773#issuecomment-876705521)). However, the proper fix would seem to be for VS Code to always append language ID's when looking up semantic token fallback scopes.