InputManager: Update docs for pilferPointers

Pilfer pointers from a window based on the current gesture stream. If any new pointers go down within the touchable region of the pilfering window and are part of the same gesture, those new pointers will be pilfered as well, and will not be sent to any other windows.

Pilfering is designed to be used only once per gesture. Once the gesture is complete (i.e. on ACTION_UP, ACTION_CANCEL, or ACTION_HOVER_EXIT), the system will resume dispatching pointers to the appropriately touched windows.

NOTE: This method should be used with caution as unexpected pilfering can break fundamental user interactions.

NOTE: Since this method pilfers pointers based on gesture stream that is currently active for the window, the behavior will depend on the state of the system, and is inherently racy. For example, a pilfer request on a quick tap may not be successful if the tap is already complete by the time the pilfer request is received by the system.

Bug: 347700797
Bug: 245989146
Change-Id: I33a7cf7bdf69a171c82b887bdaa3922c311467ce
Test: None
Flag: DOCS_ONLY