Add FindUsagesOptions and thread option getter through FAR services

[tmat]

Depends on https://devdiv.visualstudio.com/DevDiv/DevDiv%20Team/_git/TypeScript-VS/pullrequest/376624

Follow up: #59168

[CyrusNajmabadi]

not sure how i feel about thsi change. it doesn't feel intuitive to me (yet) that options are part of a context object (which is intended to push results into as the find progresses).

[tmat]

not sure how i feel about thsi change. it doesn't feel intuitive to me (yet) that options are part of a context object (which is intended to push results into as the find progresses).

We need to be able to call back to the in-proc impl to fetch the options lazily because we do not know upfront what languages are we gonna find the references in and we do not want to pre-fetch the options for all languages.

Context is created at the entry point of the feature on the client and thus has access to the client options.

[CyrusNajmabadi]

I want to be on the same page here. What option does findrefs need? I'm surprised you hear that it would depend on anything lang specific.

[tmat]

Classification options. The SourceReferenceItem passed to OnReferenceFoundAsync are classified using the language's classification options.

[tmat]

Interesting: SerializableDocumentSpan does not serialize Properties of DocumentSpan that may contain classification spans.

[CyrusNajmabadi]

Classification options. The SourceReferenceItem passed to OnReferenceFoundAsync are classified using the language's classification options.

Bleagh... there are times when i wish things were not lang-specific options.