R1:72f82abe0723

Improve recovery from panel action rendering exceptions, and mark "Changeset" queries as not suitable for panel generation

Summary:
Fixes T13443. When a panel raises an exception during edit action generation, it currently escapes to top level. Instead, catch it more narrowly.

Additionally, mark "ChangesetSearchEngine" as not being a suitable search engine for use in query panels. There's no list view or search URI so it can't generate a sensible panel.

Test Plan:
- Added a changeset panel to a…