lv_arc_angle_within_bg_bounds() function

Check if angle is within arc background bounds In order to avoid unexpected value update of the arc value when the user clicks outside of the arc background we need to check if the angle (of the clicked point) is within the bounds of the background. A tolerance (extra room) also should be taken into consideration. E.g. Arc with start angle of 0° and end angle of 90°, the background is only visible in that range, from 90° to 360° the background is invisible. Click in 150° should not update the arc value, click within the arc angle range should. IMPORTANT NOTE: angle is always relative to bg_angle_start, e.g. if bg_angle_start is 30 and we click a bit to the left, angle is 10, not the expected 40.