Support uBit.display.animate() negative stride

[microbit-carlos]

Request in MakeCode:

• Negative scroll image value does not function on micro:bit microsoft/pxt#3485

Issue reported in DAL with a longer discussion:

• Issue: Animate function does not work with negative stride microbit-dal#351
• PR: MicroBitDisplay::animate - Support negative stride microbit-dal#427

And PR submitted for CODAL:

• AnimatedDisplay animate - support negative stride codal-core#145