Add support for dependency tags

Primary builder logic is becoming complicated due to the two pass nature
of mutators that add dependencies and GenerateBuildActions that handle
the dependencies.  The reason why the dependency was added is lost by
the time GenerateBuildActions is called, resulting in build logic that
has to recreate all the dependencies and try to match them up to the
modules returned by VisitDirectDeps.

Change the API of AddDependency to take a DependencyTag interface, which
is satisifed by anything that embeds BaseDependencyTag.  Mutators and
GenerateBuildActions that call VisitDirectDeps can pass each Module to
ctx.OtherModuleDependencyTag to retreive the DependencyTag that was
passed when adding the dependency.

Change-Id: I0814dcd26d1670302d340b77e8dc8704ed7b60bf