Re-add `TestScreenCaptureStream` implementation for `mock_client` to fix FreeBSD and MinGW builds (#35191)

The implementation was removed in #31506. re-added it to match the
current implementation from `gpui::test`

Closes #35189

Release Notes:

- N/A
3ad0546b0dMaksim Bondarenkov committed on 7/28/2025, 12:02:48 PM· committed by GitHubparente38f575
1 file changedLine totals unavailable