v1.2.0 breaks matrix.clear() when using Arduino R4 LED Matrix with matrix.set(...)

[stefanmarks]

The v1.2.0 update of the Arduino LED Matrix library broke the clear() command in that it clears the frame buffer, but not the canvas buffer.

That was previously done (admittedly in a crude way) by setting all pixels off one by one in the base ArduinoGraphics class, but does not happen anymore in the overridden method.
A simple additional memset() in clear() should resolve this issue.