KeyguardQuickAffordanceConfig: some renames

Some renames to make the interface a bit friendlier to upcoming
customizable quick affordances work and match the design document.

Bug: 254858696
Test: all tests pass. Ran system UI on device, saw home controls
affordance still shows up, animates to fade when lock-screen transitions
to unlocked, and opens its target activity when clicked.

Change-Id: Ic90ea1463540a438ed296745916385e4959597c0