Center scroll wheel zoom on mouse pointer

[pmjobin]

This modifies the behaviour of scroll wheel zooming so that it mimics other map packages (such as Google Maps) by pinning the center of scaling under the mouse pointer. This works regardless of the rotation of the map.

[JaffaKetchup]

@pmjobin Will try to test soon. Thanks for your contribution!

[JaffaKetchup]

To be able to merge this, the checks need to be satisfied. To do this, please run dart format . --fix in your console.

[JaffaKetchup]

@pmjobin @a14n How will #1191 and #1182 work together? Will they interfere?

[JaffaKetchup]

Sorry to keep annoying you! This also needs to be fixed to appease the checks:

lib/src/gestures/gestures.dart:3:[8] - unused-import - Unused import: 'dart:math'. Try removing the import directive. 

[JaffaKetchup]

Will test changes soon, now auto-checks are all good :)

[pmjobin]

Thanks for your help!

[ibrierley]

Nice work and thanks! Tests good for me with and without rotation in chrome and android.

[JaffaKetchup]

Testing now...
Will have to resolve those conflicts before merge.

[a14n]

To resolve the conflict you have to replace MapEventSource.custom with MapEventSource.scrollWheel

[JaffaKetchup]

LGTM, seems to work.