encodedSemanticClassifications-full does not request cancellation when completions are requested

[sheetalkamat]

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Steps to Reproduce:

Does this issue occur when all extensions are disabled?: Yes/No

Found this while investigating microsoft/TypeScript#35364 which turns out that semantic colorization takes approximately 10s but completions are quick with or without that request but seem to take longer as colorization is not cancelled.

[mjbvz]

I investigated this a while back but a full fix turned out to be quite complicated (mainly because we need to first cancel and then re-queue the request)

5942862 makes it so that these requests are canceled whenever the document changes. So if the user is relying on quick-suggestions while typing, these requests should already be getting canceled. However they could still hit an issue if they simple trigger suggestions without typing. I think this is acceptable given the complexity of a complete fix

[mjbvz]

Reopening based on TS team's desire the prioritize this