[Request] Provide file-specific onDidChangeSemanticTokens event

In C/C++, when a modification is made to a header file, semantic tokens in files that include it could change. (i.e. when renaming a function). Because those other files are not themselves changing, VS Code does not re-request tokens for them (if also open). There is an `onDidChangeSemanticTokens` event we can use to indicate that tokens have changed. However, this event is not specific to a file, so may cause token requests for files that don't require an update. Could an additional event be added that allows us to indicate the specific file that needs tokens re-requested? i.e. ``` onDidChangeSemanticTokensForFile?: Event<Uri>; ```