[WindowDecor] No-op keyboard shortcut for toggling from fullscreen

when the task is mid-drag. This is a short-term fix for fixing the crash
caused by a race condition when a fullscreen task is being dragged to
freeform (before dropping) and using the keyboard shortcut to toggle the
task to freeform. In this case, the windowing mode has already updated
to freeform due to the keyboard shortcut toggle, but
onDragPositioningEnd still sees a TO_DESKTOP drag indicator.

This CL disables the keyboard shortcut toggling of the windowing mode if
the task being toggled is the task that is mid-drag to freeform.

Fixes: 444264266
Test: atest WMShellUnitTests:com.android.wm.shell.desktopmode
Flag: EXEMPT BUGFIX
Change-Id: I7a8f114542b7ad3428e68018052899f954599289