New tool: Rounded box

[sbrin]

Implement new Rectangle property: Rounded corners

Rectangle layer should have a checkbox to enable-disable rounded corners.

It has native u8g2 support:

drawRBox drawRFrame

AdafruitGFX has it as well: drawRoundRect & fillRoundRect

FlipperZero:

canvas_draw_rframe(canvas, x, y, width, height, radius)
canvas_draw_rbox(canvas, x, y, width, height, radius)