Remove exposed hidden apis in Point.java

Point is moving into the UI/graphics module, so hidden apis need to be
cleaned up:
* printShortString is now publicly exposed and renamed to Point#dump, to
mirror already public APIs such as TokenWatcher#dump
* The two convert methods have very few users and their implementations
are both trivial and only rely on the existing public API, so they are
in-lined directly in the callers.
* Introduce a GraphicsProtos utility class living outside of the module
that just converts Graphics parcelables into protobuf objects. Currently
WindowManager and the view system dump protobuf representations for
debugging. Accordingly GraphicsProtos is a hidden public class, as the
protobuf representation of the graphics classes are not publicly
exposed and should be considered an implementation detail of the system.

Bug: 152804266
Test: boots, builds
Change-Id: I5e25dbbe47b3c690d7d763a0082beb8d8a9c86d3