Fix rounded corner padding for external displays

Use a small hardcoded padding for the rounded corner content padding on external displays, instead of 0.

This provides a better default for external displays that don't have rounded corners, preventing UI elements from being attached to the edge

Bug: 439598525
Test: Show statusbar on external display, verify the left part is not attached to the beginning
Flag: EXEMPT minor visual fix
Change-Id: I0d56814ec422e5a3fcf04b366d6c022c1946c885