Provide a set of document highlights, like all occurrences of a variable or all exit-points of a function.
The document in which the command was invoked.
The position at which the command was invoked.
A cancellation token.
An array of document highlights or a thenable that resolves to such. The lack of a result can be
signaled by returning undefined, null, or an empty array.
The document highlight provider interface defines the contract between extensions and the word-highlight-feature.