DO NOT MERGE: Use prebuilts of the ART Module by default (reland 2).

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 http://ag/15200786 after fixing various build issues (see tests).
Using DO NOT MERGE to limit presubmit use to the branches for which
prebuilts were updated in http://ag/15189174 and http://ag/15200785.

Test: Heavy presubmits on build_test{,2,3,4} and flame-userdebug
Test: Heavy presubmit on mainline_modules-userdebug on sc-mainline-prod
Bug: 192542393
Change-Id: Id6800fe3564149e6c555b5f68a41b01e9c7dff3f

core/android_soong_config_vars.mk

@@ -70,7 +70,7 @@ else
   # This sets the default for building ART APEXes from source rather than
   # prebuilts (in packages/modules/ArtPrebuilt and prebuilt/module_sdk/art) in
   # all other platform builds.
-  SOONG_CONFIG_art_module_source_build ?= true
+  SOONG_CONFIG_art_module_source_build ?= false
 endif
 
 # Apex build mode variables