Make FlingInfos unique.

Under test, velocities are often identical, which causes StateFlows not to emit duplicate values. Other sources of uniqueness such as SystemUptimeMillis also don't behave as expected under test, so this seems as good a way as any to address that.

Test: atest KeyguardTests
Flag: N/A
Bug: 278086361
Change-Id: I0d67470d894928e47e6489d9101e788c1eab51d5