Ignore prebuilt apexes if PRODUCT_MODULE_BUILD_FROM_SOURCE is true

Some devices would like to use sources of mainline modules
even in next builds. This CL uses PRODUCT_MODULE_BUILD_FROM_SOURCE to
ignore the apex_contributions specified in the shared google_device's next.scl

Long term, this will be implemented by creating a product specific
release config map for this family of devices

Test: lunch <device>_fullmte-next-userdebug && m nothing
Bug: 325666427
Ignore-AOSP-First: The CL touches an internal only allowlist
Change-Id: I0cabba5faa4535dcdff3aa8b87aa61ac06ac9edb