Add a trace_references_from dex optimization property

Introduce a new property `trace_references_from` in the optimize block.
This field allows specifying a set of downstream targets from which to
trace references when optimizing the current target.

In practice, this requires explicit breaking of any cycles that might
occur. A follow-up effort will explore doing this dynamically and
implicitly for `libs` references onto an optimized target that
enables this feature.

Bug: 212737576
Test: m nothing
Test: go test ./java
Flag: EXEMPT bugfix
Change-Id: I088bd8bf89403661a084a43b2822a6efbbc0294d