DO NOT MERGE: Use prebuilts of the ART Module by default (reland).

This means prebuilts located in
/vendor/unbundled_google/modules/ArtGooglePrebuilt and
/prebuilts/module_sdk/art are used instead of sources in /art,
/libcore, and /libnativehelper.

Sanitizer and coverage builds builds are excluded, as are builds using
the products art_module_*, armv8, arm_krait, and others in
device/generic/art.

To keep using ART and libcore sources in local builds, set
SOONG_CONFIG_art_module_source_build=true. See art/build/README.md for
further info.

This relands http://ag/13552665 after updating ART prebuilts
(ag/15189174, ag/15200785). Using DO NOT MERGE to have the same scope
as they do.

Test: presubmits
Test: vendor/google/build/build_mainline_modules.sh
  with a line
    build/soong/soong_ui.bash --dumpvar-mode \
      SOONG_CONFIG_art_module_source_build
  directly before the module build commands in
  build_unbundled_mainline_module.sh and check that it's still true.
Bug: 192542393
Change-Id: I6281ef27bf9cdcb2ad5112b8a0932e4201d69dc2