Add support for multiple SemanticTokensProvider, [possibly other providers too]

[REYNEP]

Currently a lot of providers [e.g. DocumentSemanticTokensProvider] supports a single one. if multiple are registered the best matching one is chosen.

So no 2nd extension can add tokens along with 1st extension's tokens.

The Feature

Add support for multiple SemanticTokensProvider, [possibly other providers too].... so that, a extension can add stuffs on top of another.

Some may ask, 'Why?'. Bcz semanticTokens are more like for IntelliSense, and running multiple different IntelliSense is not a good performance Idea.

But, there could be a single running Intellisense & LanguageServer that two different extensions could be using, and both of those could be like adding different kinds of SemanticTokens....