Drop multi-window mode requests in locked task mode

It used to throw UnsupportedOperationException, but in cases when the
WCT/transition request is queued, it ends up crashing system_server.
Since locked task mode is not something WM shell controls, WM shell
can't fully prevent from setting multi-window mode in locked task mode.
Therefore we shouldn't crash any processes for that.

We should also extend this no-throw principle to other scenarios where
WM core can't fulfill certain operations in WCT for some internal states
of which WM shell doesn't have full control. I didn't find other such
throws in current code base in a quick check, so this CL only changes
this one.

Use warning to match the other logging level in the original commit
a9201bcf where this throw was added,
also for the reason that WM shell can't fully prevent it from happening.

This CL also reverts 462b8f5f because it
was made to avoid throwing this UOE in a particular situation.

Bug: 263492303
Test: Build and boot.
Change-Id: I188abae4b1992ba66fe31eadc886b2c0586640f9