fix(amazonq): do not auto trigger if the ongoing typeahead does not match

[leigaol]

Problem

Bug: When inline suggestion is active but user types a character that does not match the typeahead, this typing event triggered a inline completion API call that eventually did not manage to display suggestion on screen, which eventually reported as rejected completions.

Solution

Previously, before Flare migration, we had this design:

https://github.com/aws/aws-toolkit-vscode/blob/amazonq/v1.74.0/packages/amazonq/src/app/inline/activation.ts#L108

Auto trigger will be disabled if at that moment the suggestion is visible.

Under the previous design, the first character that does not match the typeahead will not make a new auto trigger, it simply rejects the current inline completion.

This PR is to bring back the old design.

It is not customer facing, hence no change log.

---

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[amazon-inspector-ohio]

⏳ I'm reviewing this pull request for security vulnerabilities and code quality issues. I'll provide an update when I'm done

[github-actions]

• This pull request modifies code in src/* but no tests were added/updated.
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• This pull request implements a feat or fix, so it must include a changelog entry (unless the fix is for an unreleased feature). Review the changelog guidelines.
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[amazon-inspector-ohio]

✅ I finished the code review, and didn't find any security or code quality issues.