Set BUILD_FROM_SOURCE_STUB=true for finalization

Build from text stub feature was initially implemented to improve build
performance and may be unstable for api finalization, as the stubs
generated from api signature files miss some methods, which may cause
backward compatibility issues. Therefore, this change disables building
from text stub for api finalization.

Test: build/tools/finalization/finalize-aidl-vndk-sdk-resources.sh and inspect generated ninja file to verify that the stubs are generated from source Java files.
Bug: 310279899
Change-Id: I9d374e973788bc97514815f64eeb949a94a97647