feat(amazonq): support select images as context

[yzhangok]

Problem

WebView emit event to open system file dialog to use the VSC api to open file dialog, and the event need to be handled by extension

Solution

1. Register the request between WebView and language server by adding case OPEN_FILE_DIALOG
2. Add handling for event when language server request to open system file dialog, which is defined in languageClient.onRequest(ShowOpenDialogRequestType.method, async (params: ShowOpenDialogParams)

---

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[github-actions]

• This pull request modifies code in src/* but no tests were added/updated.
  • Confirm whether tests should be added or ensure the PR description explains why tests are not required.
• 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.
  • Note: beta or "experiment" features that have active users should announce fixes in the changelog.
  • If this is not a feature or fix, use an appropriate type from the title guidelines. For example, telemetry-only changes should use the telemetry type.

[leigaol]

don't merge unless CI passes

[laileni-aws]

what happens if vscode.Uri.parse(params.defaultUri) fails? Do we throw any error to the user or log it ?

[laileni-aws]

I guess we need to have a changeLog for this!

[laileni-aws]

LGTM