InputManager: Expose pilferPointers API

We can only migrate existing gesture monitors to spy windows if we allow
pilfering from these spy windows. Expose the pilferPointers API so that
other processes can pilfer from arbitrary input windows.

The pilferPointers API is guarded with the MONITOR_INPUT signature
permission.

Bug: 257977069
Test: Build
Change-Id: Ice43ed420502ce3b5e5d37d9ac9e810a51ed07bc