codemirror: Fix aria-label for search query input
Created by: fkling
In #36308 GitStart added 'aria-label' by mutating the DOM but the documentation explicitly says that this shouldn't be done. Using the EditorView.contentAttributes facet is the way to go.
role='textbox' is already added by CodeMirror itself.
Test plan
Inspected the DOM
App preview:
Check out the client app preview documentation to learn more.