Add new attribute to hotseat specs

Edge padding is used as the space between hotseat and the edge of the screen. In most cases it is used in a height spec, but for vertical bar, i.e. when a handheld is in landscape, it is used a width spec.

Fix: 292204436
Test: CalculatedHotseatSpecTest
Test: HotseatSpecsTest
Test: DeviceProfileResponsiveAlternativeDisplaysDumpTest
Test: DeviceProfileResponsiveDumpTest
Flag: ENABLE_RESPONSIVE_WORKSPACE
Change-Id: Ib75ffcdd33925ee9ef156dcb70eefd133c9b458b