Enable UFFD GC by default for Android U and above.

Bug: 251150519
Test: atest art_standalone_odrefresh_tests
Test: (Tested on main) -
  1. Build with OVERRIDE_ENABLE_UFFD_GC=false
  2. See odrefresh triggered on the first boot.
  3. See "Using CollectorTypeCMC GC".
Test: (Tested on UDC) -
  1. Build and install the ART APEX.
  2. See odrefresh triggered on the reboot.
  3. See "Using CollectorTypeCMC GC".
Change-Id: I212f08fa4d51b4cdac3baedd922df815cd270581