search: Update webapp to reflect new `has` syntax for predicates
Created by: tbliu98
Stacked on #40763 Part of https://github.com/sourcegraph/sourcegraph/issues/39767
Query completion suggests predicates using the has syntax instead of contains, e.g. repo:has.file.
Add hovers and decoration for repo:has and file:has predicates.
Update reference panel to use has predicates as examples.
Test plan
Added some unit tests for hovers.
Manually checked hovers, decoration, completion, reference panel.
