Trace downstream references when optimizing services.jar

Add a hook to trace references from PRODUCT_SYSTEM_SERVER_JARS
that depend on the services.jar. This ensures that services.jar keeps
such references during optimization, avoiding the need to manually
specify and update associated keep rules.

A follow-up change will remove existing hardcoded rules for certain
devices that are no longer necessary.

Bug: 212737576
Test: m + presubmit + inspect proguard_configuration for services.jar
Flag: EXEMPT build refactor
Change-Id: Idab5e6ba282c6178cff52a8cf30dda6f2a541962