Show error message on CAPTCHAs and extension errors

Previously editor would silently fail in those unsupported scenarios.
This commit does not fix bugs 52047 and 52049, it only makes the editor
behaviour more predictable and prevents users from losing their edits
completely.

Also log those cases as errors in event logging (with error code if
available).

Bug: 52047
Bug: 52049
Change-Id: I5494063a86d8c9f732eb05a007fdac903e2e6b20
Merge "Show error message on CAPTCHAs and extension errors"