SurfaceFlinger: Implement drop input modes

ALL: If this mode is set on a layer, set the DROP_INPUT
feature flag on the layer and its children if it has a valid input
channel. This will ensure these layers will not be able to receive any
input.

OBSCURED: If this mode is set, set the DROP_INPUT
feature flag on the layer and its children if they have a valid input
channel and they are considered occluded. This can happen if the layer
has a alpha set by it's parent OR if its buffer has been cropped by its
parent. Otherwise, the input feature flag DROP_INPUT_IF_OBSCURED flag
will be set so inputflinger can decide to drop input based on
occlusion.

Test: atest libgui_test InputDispatcherDropInputFeatureTest
Bug: 197364677
Merged-In: Ibce11ee7df5b5c8c226ebfab29574a99cd656f6d
Change-Id: Ibce11ee7df5b5c8c226ebfab29574a99cd656f6d