Treat Bluetooth-smoothened events with modified timestmaps as synthetic

Since we are modifying the timestamps of events from Bluetooth devices,
these may have unintended consequences on latency metrics. Treat these
modified events as synthetic by setting the event time equal to the read
time to give it zero read latency.

Bug: 257124950
Test: atest inputflinger_tests
Change-Id: I65288050b273e6544861af1db0aee7a42d1b246d