Determine whether to enable userfaultfd GC at build time.

This is determined by:
- a product config flag
- the vendor API level

It is then passed to the device as a system property
"ro.dalvik.vm.enable_uffd_gc".

This change is a no-op change. It doesn't enable userfaultfd GC by
default. OVERRIDE_ENABLE_UFFD_GC=default can be passed to the build
system to enable userfaultfd GC for testing purposes.

Bug: 242553398
Test: -
  1. lunch aosp_redfin-userdebug
  2. OVERRIDE_ENABLE_UFFD_GC=default build/soong/soong_ui.bash --dumpvars-mode --vars=ENABLE_UFFD_GC
  3. See "false" in the output
Test: -
  1. lunch aosp_oriole-userdebug
  2. OVERRIDE_ENABLE_UFFD_GC=default build/soong/soong_ui.bash --dumpvars-mode --vars=ENABLE_UFFD_GC
  3. See "true" in the output
Test: -
  1. lunch aosp_redfin-userdebug
  2. OVERRIDE_ENABLE_UFFD_GC=true build/soong/soong_ui.bash --dumpvars-mode --vars=ENABLE_UFFD_GC
  3. See "true" in the output
Test: -
  1. lunch aosp_oriole-userdebug
  2. OVERRIDE_ENABLE_UFFD_GC=false build/soong/soong_ui.bash --dumpvars-mode --vars=ENABLE_UFFD_GC
  3. See "false" in the output
Change-Id: Ifd6e6cddb502315912ff949619a5b526ae0d73ff