Allow disable() mid-drag (#2419)

[krabbypattified]

This code allows the user to call dragPan.disable() mid-drag.
This is intended as a fix for touch (mobile) devices.
It enables draggable markers on touch devices.

[mollymerp]

@krabbypattified thanks for your contribution! the tests are failing because of linting errors right now. you can fix this by running yarn lint --fix or npm run lint -- --fix.

do you have a test case that you used to manually determine if this fix was working? I can investigate adding a unit test to test this fix as well.

[krabbypattified]

@mollymerp I've added a test for my code, but since there's no simulation.touch events, I wasn't able to include touch tests.

I've run yarn lint --fix which has come back with no errors. Granted, I did copy/paste from my local Atom files into the GitHub online commit system.

[krabbypattified]

Why is Flow doing this to me?
if (e.touches) return this._onTouchEnd(e); ^ MouseEvent. This type is incompatible with the expected param type of 195: _onTouchEnd(e: TouchEvent)

[mollymerp]

Ooo @krabbypattified sorry for the delay here. What's happening is that since you're not explicitly ensuring that e is of type TouchEvent before invoking _onTouchEnd flow thinks that the e passed to _onTouchEnd could possibly be of type MouseEvent.

I belive you can get rid of this error by changing your condition on L111 from if (e.touches) to if (e instanceof TouchEvent)

[jfirebaugh]

Thanks for the contribution @krabbypattified, and sorry that we weren't more responsive on this PR. It got overtaken by other event-related work, so I've opened an alternative fix for the issue in #6232.