Move EventBuilders.h next to MotionEvent definitions

This allows these builders to be accessed by code in other locations,
which is useful for writing other tests.

Test: `atest frameworks/native/services/inputflinger/tests/InputDispatcher_test.cpp`
Test: `atest frameworks/native/services/inputflinger/tests/InputDeviceMetricsCollector_test.cpp`

Bug: 268245099

Change-Id: I7bca675e0b83673a30db2f1c06abda4369b69c42