Upgrades JS CallbackControl.onPostback - better logging on exception

[belisoful]

Callback dispatch: log on failure, fall back to the default action

CallbackControl.onPostBack (and TActiveImageButton) previously called dispatch() then preventDefault(). If dispatch() threw — typically from a ClientSide hook — preventDefault() never ran, so the failure was silent and the click still fell through to a postback.

Now the dispatch is wrapped: on throw, the error is logged via Logger.error and rethrown, and preventDefault() is deliberately skipped so a submit button degrades to a full-page postback instead of dead-ending. TActiveImageButton keeps its x/y coordinate inputs on failure so the fallback submit carries the click position.

JS-only; no PHP change. Adds unit coverage in activecontrols.test.js and a functional spec (TActiveButtonPostBackFallbackTestCase).

[belisoful]

The Agents identified that if there is an exception, that "preventDefault" is not called and falls back to posting the page. Any exception is written to the JS log as a matter of the browser function... but it would immediately be erased by the post response. Any intrinsically logged exceptions are unknown and unrecoverable.

This PR makes the logging of the exception deliberate and known.

The agents recommended rearranging the order of operation, but after considering the pros and cons, the way it is works but needs better exception handling.