fix(amazonq): improve typeahead experience

[leigaol]

Problem

In the inline flare branch, the typeahead experience is bad because even when user typed matching characters after seeing a suggestion, we are still re-fetching the new suggestions, which causes the cached suggestion to disappear and new suggestion re-appear.

Solution

Use the previous suggestion from last invocation if what user typed matches the suggestion prefix.

typeahead.mov

This also aligns the experience in prod plugins without Flare inline.

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[github-actions]

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