Add utils to process a11y check results

Also moved a11ychecker from core/... to services/accessibility

NO_IFTTT=New IFTTT

Bug: 350530488
Bug: 341926585
Test: unit tests
Flag: com.android.server.accessibility.enable_a11y_checker_logging
Change-Id: Ibc0cb4eb2d207032ef21a46196d4b2cc04cf7e95