'moveend' fires during multi-touch gesture input

[kristfal]

Issue

The moveend event behaves differently during single-touch and multi-touch input.

During single touch, the moveend event is fired when the gesture finishes (finger is no longer touching the screen). During multi-touch, eg. two fingers touching the screen at the same time, moveend is fired on every single animation frame for the duration of the gesture.

mapbox-gl-js version: Master

Steps to Trigger Behavior

1. Bind an event listener to 'moveend'
2. Two finger rotate / pinch on a mobile device
3. The event listener will now fire during the pinch / rotate gesture

Expected Behavior

'moveend' fires when user gesture is finished and any optional inertia have stopped playing during both multi-touch and single-touch gestures.

Actual Behavior

'moveend' fires constantly during multi-touch user gestures and at the end of single-touch gestures.

Tested in iOS10 Safari and Android Chrome.

Kinda related to #1104

[lucaswoj]

This is effectively a duplicate of #3357. "move" has to do with Camera state changes, not necessarily interaction handler state changes.

[lucaswoj]

Added a bullet point to #3357 to explicitly capture the essence of this ticket

prevent interaction handlers with inertia from firing multiple moveend events within an individual interaction