Cleanup classic autocomplete context

[beatlevic]

Remove obsolete context tracking and cleaning up types.

• Simplifies getFromLLM() method:
  The method extracts prefix, suffix, and languageId from the context, but these could be passed directly since they're already available in the caller.

• Reduces duplication in contextToAutocompleteInput():
  The function extracts prefix/suffix which is already done in the caller.

• Simplifies context building:
  Since we're building the context in provideInlineCompletionItems and immediately converting it to AutocompleteInput,

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Latest commit: 9449534

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[markijbema]

Either AutocompleteInput needs to be the input to the inline completion provider, or we should just ignore the type; the whole goal of using it as input is that we have better compatibility with the continue inline completion provider.

Currently we don't use that as we use continue from a higher level, however, we might still want to move towards this way as we don't have continue tied into the rest of our system, and this might hinder that

[markijbema]

ive added some suggestions for further cleanup, but they're also slightly out of scope, so fine with merging as is and doing that separately