Improve the messaging in our unidentified action exceptions.

[barryhughes]

We trigger InvalidArgumentExceptions from a number of locations, all with the same basic message:

Unidentified action <ID>

This is not particularly helpful, and conveys no information about what was happening at the time the exception was thrown. This change adds some additional context to a number of these exception messages.

Updates #1059 (but does not close).

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Testing instructions

This PR changes the text of various exception messages, but there are no functional changes to the way the library works. Manual testing will therefore have limited value, but I've still provided some basic instructions to see the change in action.

✍🏼 Note that you need to have access to the system/PHP error log, or some other way to view errors logged via error_log() calls:

1. Open Tools ‣ Scheduled Actions
2. Open the very same screen in a second browser tab.
3. Identify and check the box for the same action in both browser tabs.
4. Using the bulk actions, delete the action first in one tab and then the other.
5. You should see something similar to the following being logged:

Action Scheduler was unable to delete action 12345. Reason: Unidentified action 12345: we were unable to delete this action. It may may have been deleted by another process.

If that seems a little verbose, note that the first half (everything before Reason:) is added by the List Table implementation when it catches the exception.

Changelog

Fix - Provide more context when throwing InvalidArgumentException exceptions.

[jorgeatorres]

LGTM. Thank you @barryhughes!