Expose onDoubleClick() callback

[mkmckenna]

This exposes an onDoubleClick() callback function allowing the user to override the default functionality of MapCompose.

This is a proposed solution to #149

I have included a small demo example, however this can be removed before merging.

[p-lr]

Thanks but I had a different idea in mind. Something like what is done for ClusterClickBehavior. i.e the ability to set a custom callback but also retain the default behavior, optionally.

[p-lr]

To be more precise, with having this api:

fun MapState.onDoubleTap(withDefaultBehavior: Boolean, doubleTapCb: (x: Double, y: Double) -> Unit) {
    this.doubleTapCb = doubleTapCb
}

[mkmckenna]

No problem. I'll keep an eye on the issue.