Resolving duplicate “Fingerprint Sensor” talkback in Side-FPS SUW

Prevents Talkback from announcing “Fingerprint Sensor” twice in the
side-FPS fingerprint enrollment page in setup wizard. Two accessibility
events that speak “Fingerprint Sensor” are sent when the Talkback focus
lands on the sensor location indicator, so we override the
AccessibilityDelegate dispatcher to intercept and ignore the first
event.

Fixes: 209933998
Test: atest SidefpsControllerTest
Change-Id: Ib5fad6dc0b36eb69b6084296956c12a9b25e28bb