InputFlinger: Add DROP_INPUT and DROP_INPUT_IF_OBSCURED feature flags

If a window has the feature DROP_INPUT set, then all touch and
key events directed to the window will be dropped. For touch events,
the events will not go to the window behind it.

If a window has the feature DROP_INPUT_IF_OBSCURED set, then all
touch and key events directed to the window will be dropped if
the window is considered partially or fully obscured.

These flags are used to enable features that allow for a less trusted
interaction model between apps. See the bug for more details.

Test: atest libgui_test InputDispatcherDropInputFeatureTest
Bug:197364677

Merged-In: I71d7cf5064c8ce4626cff09b92e15ca38b39cbbe
Change-Id: I71d7cf5064c8ce4626cff09b92e15ca38b39cbbe