[Feat] Flip Icon along X or Y axis

[TextTL]

Target Use Case

Currently, IconLayer has getAngle for rotation of Icon. In many cases, mirror an icon along X or Y is necessary. For example, if we have an icon, __/ __, and want to render as __ \____, rotation does not work. Adding accessor to flip an Icon along X or Y axis is a useful feature in this case.

Proposal

add an accessor getFlip() null - no flip, 0 flipX, 1 flipY or 'X" or "Y"