search: Port server side query validation to frontend

Created by: fkling

See #24689 (closed)

This adds validation for commit/diff filters, repo+rev filters and structural search. The validation isn't triggered when the pattern search type is changed via the buttons. That's because the validation logic is only triggered when input changes. Something to consider for the future.

https://user-images.githubusercontent.com/179026/133822215-6d43fe98-2a71-4fa4-a478-0ba66233d12e.mp4