Expand the displayFrame for shadows

Bug: 185799825
Test: manual
Test: libcompositionengine_test

Some HWCs crop to the displayFrame. A shadow layer uses its
geometry.boundaries (possibly cropped by geometry.cropRect) as the
size of the object casting a shadow, so the shadow may not be contained
by the displayFrame. For a shadow, expand the displayFrame out by the
shadowRadius to prevent cropping of the shadow.

Change-Id: I8b6c7953d05718a89bdbc59d57775e52195a8131