[5/n] Camera Compat UI: Unify margins logic for camera and size compat controls.

Before this change, margin between a hint and a camera compat control was smaller than required 8 dp while for a size compat control it was bigger than 8dp (since ag/16420818). This change makes them consistent and also simplifies layout definition for the size compat button by declaring margings explicitly rather than including them in width and height implicitly.

Test: manual
Bug: 206602997
Change-Id: I09839e764d2c8904954a594433888bfdc21d56ba