Add Toggle to search only within open buffers

[elementsuite-gregor]

Check for existing issues

• Completed

Describe the feature

I have come to rely on this feature(open buffer search) in vscode recently. Having all feature related buffers open in tabs, I can then quickly search for more generic keywords e.g. "time", "setDate" which would yield thousands of results on the full project search.

If applicable, add mockups / screenshots to help present your vision of the feature