[FEATURE] Add catch-all `MapEventZoom`

[opk12]

What do you want implemented?

A generic "zoom" event, to simplify updating the internal state of the app that depends on the zoom level number.

What other alternatives are available?

Currently the app must enumerate all the gestures: zoom in and out buttons, MapEventDoubleTapZoom, MapEventScrollWheelZoom.

This approach

• does not handle the pinch zoom event; I'm told that there is a multi finger event that is redirected into a MapEventMove, but this is easy to miss in the API
• ignores future gestures: the two-finger tap requested in #1432
• is verbose

Can you provide any other information?

No response

Severity

Annoying: Currently have to use workarounds