Do not perform invisible transitions while the screen is off.

This change caches whether launcher was active at the time of the screen
off, and assumes this last state when the screen is actually off.

While trying to understand the code, I renamed a couple class-internal
methods and flags, plus added comments. If they are not accurate, its
due to a misunderstanding on my part, and I will gladly revisit and
check whether all the assumptions I made still hold.

Bug: 261418621
Test: manually

Change-Id: I2ad25caf478100781a063c356c5fd2d20d3e1917
Merged-In: I2ad25caf478100781a063c356c5fd2d20d3e1917