Use ART_MODULE_BUILD_FROM_SOURCE instead soong config variable

When product configuration is converted to Starlark, soong config
variables will be stored in a dictionary and won't be able to be
specified directly on the command line. Use a regular variable
that controls the soong config variable.

Bug: 220940864
Test: Presubmits
Change-Id: I5622d9e626e2cf84afe67cd2a214530e64cefc3e