Add benchmark for onWindowInfosChanged

This benchmark should not have any socket writes, and will help us
detect whether the high variability of results we are seeing in the
other two benchmarks could potentially come from that.

Results:

arm64-v8a inputflinger_benchmarks: Passed: 3, Failed: 0, Ignored: 0, Assumption Failed: 0,
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Benchmark                             Time         CPU       Iteration
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
inputflinger_benchmarks:
  #benchmarkNotifyMotion            125573 ns    90766 ns         5699
  #benchmarkInjectMotion            123218 ns    91416 ns         6341
  #benchmarkOnWindowInfosChanged     10888 ns    10000 ns        65385

Bug: 210926970
Test: atest inputflinger_benchmarks (see results above)
Change-Id: I1d0b6f00c3d4fa74188c7493129ed9515f3246d2