feat(amazonq): show a message when no suggestions are found on manual invoke

[Hweinstock]

Problem

When manually invoking inline suggestions, it is possible for the backend to still not reply with results. Since the user took an action to invoke this, we should let them know when it fails.

Solution

• add a message with same timeout as original implementation.

Testing and Verification

• added unit test.
• E2E flow demo (notice it doesn't trigger on automatic failures, but does on manual invoke failures):

noSuggestionsDemo.mov

---

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[github-actions]

• 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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[Hweinstock]

This log message can help us determine if results not showing are due to vscode quirks or backend issues.

[jpinkney-aws]

instead of waiting I think you might be able to do something like this:

const p = new Promise((resolve) => {
     getTestWindow().onDidShowMessage((e) => {
         assert.strictEqual(e.message, noInlineSuggestionsMsg)
         resolve()
     })
})

and then

await p

here