SF: Tie VSyncState lifetime to display hotplug

This CL creates/destroys EventThread::VSyncState when the display is
connected/disconnected.

Bug: 74619554
Test: libsurfaceflinger_unittest
Test: dumpsys SurfaceFlinger --vsync
Change-Id: I46dad4857222b6d2932ab568c4d66325edc3371b
7 files changed