Altering TouchExplorer behavior to support Split Tap

Allows touchExplorer to broadcast a POINTER_UP event while in the touch exploration state.
On TOUCH_INTERACTION_END, TouchState transitions to touch exploration instead of clear if there are any pointers down.

Bug: 374930391
Test: atest TouchExplorerTest TouchStateTest
Test: manually verify conditions mentioned in bug do not persist.
Flag: com.android.server.accessibility.pointer_up_motion_event_in_touch_exploration
Change-Id: I33b8d992c9e47d7bd62d2242b1ddbd52d6f81df1