Add build number if TARGET_BUILD_APPS_WITH_BUILD_NUMBER is defined

This change allows unbundled app builds to embed the build number in the
version name by defining TARGET_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: I9a7e4f96f0d92c19d832933b5c68bd6b75ce9ce6