Debt - Hook up a generic textual document highlight provider for single and multi file settings

[Yoyokrazy]

Fixes: #196240

couple bugs were blocking this:

• in mainthread, would return undefined if dto was falsy or empty, but empty would come whenever a provider didn't get any highlights (ie clicking a commment in a typescript file)
• textual document highlight provider was only set up for multi file...
• first() conditions weren't taking into account the result shape being a ResourceMap correctly, size = 0 is valid

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A newly exposed issue:
scoring for language providers falls into one of three buckets:

• score: 10 is for a match on the selector
• score: 5 is for anything with language: '*'
• score: 0 is an explicit mismatch

now you have to consider, what if someone created a different textual highlight provider for whatever reason (perf, dif behavior, etc), and wanted to be scored above our default textual provider, but below a perfect match.

Could our textual fallback be scored at maybe a new score of 1? leaving room for some new heuristic to score at 5? time to think