Provide API for retrieving semantic tokens of a range

[rcjsuen]

Clients may want to only fetch the semantic tokens of the visible lines in the editor instead of the entire file. We should change the function of computeSemanticTokens so that it can optionally take a Range argument for faster processing.

dockerfile-language-service/src/main.ts

Lines 127 to 130 in 3ea186f

	/**
	* Experimental API subject to change.
	*/
	computeSemanticTokens(content: string): SemanticTokens;

export interface DockerfileLanguageService { {
    computeSemanticTokens(content: string, range?: Range): SemanticTokens; 
}