Draw shadows in root task instead of leaf task and use EffectLayer to draw shadows

Temporarily disable compositor shadows for freeform until root task has the correct/non-fullscreen bounds.

Fixes: 148807641

Test: adb shell settings put global render_shadows_in_compositor 1
Test: go/wm-smoke
Change-Id: I10371d2a2977bc4d10204d3cf4b052da5165e0e6