Preserve LED Buffer after Rotation

[203Null]

Currently, after an LED is set, it is directly written into the Device layer managed LED buffer. That means the positional info of it is lost.

When we need to rotate the buffer, we don't know the color in the buffer's XY position to conduct the rotation.
A possible solution is that the device layer will provide the system layer with an API to reverse calculate XY based on buffer index.

The implementation right now is that all buffers will be wiped after rotation. 5e7dfb7

[203Null]

I believe it's ideal for the device layer to provide an Index to XY look-up function. Otherwise, the system/application layer can not get current buffer data.

[203Null]

Currently, the OS will clear all layers upon rotation. This might not be idea in edge cases but good enough for now.