Change TARGET_BUILD_APPS_WITH_BUILD_NUMBER to a product variable

This change allows unbundled app builds to embed the build number in the
version name by defining PRODUCT_BUILD_APPS_WITH_BUILD_NUMBER, so that
APK files from a build can be easily identified.

Ignore-AOSP-First: changes in topics with internal-only projects
Test: manual build
Bug: 340311907
Change-Id: If7feda5eec2bc1e54a90b4adae1bd6da19e3ea45