Improve tracking of exported sdk libraries

The build tracks the java_sdk_library/_import modules that are
referenced by libraries so that it can ensure that any Android app that
includes code that depends on one of those modules has the appropriate
<uses-library> entry in their manifest.

Unfortunately, there were a couple of issues with that:
1) It only tracks direct references to the java_sdk_library module
   itself, e.g. android.test.mock. Direct references to the stubs
   module, e.g. android.test.mock.stubs were not tracked. Making it
   possible for Android apps to reference libraries which would not be
   available at runtime.
2) The logic for determining whether something was a java_sdk_library
   was repeated in a number of places making it difficult to allow
   java_sdk_library/_import instances to determine whether they should
   be treated as an Android shared library.
3) It tracks (and could use) even those java_sdk_library instances
   which do not represent a shared library, e.g. the ones that set
   api_only: true. While this change will simplifty fixing that the
   actual issue will be fixed in a follow up change.

Changes:
* Added EmbeddableSdkLibraryComponent and embedded it into
  java_sdk_library/_import, java_library and java_import. It provides
  the common code to minimize duplication. It contains an
  SdkLibraryToImplicitlyTrack field that if set will cause any
  references to the containing module to add the SdkLibraryParent to
  the list of implicit sdk libraries being tracked.
* Changed code that assumed that anything that implemented
  SdkLibraryDependency required tracking to use the
  OptionalImplicitSdkLibrary() method to get the optional name of the
  sdk library to track. That will allow a follow up change to return
  nil from that method to exclude an sdk library from being tracked.
* Moved SdkLibraryDependency from java.go to sdk_library.go as that is
  a better place for it to be.
* Changed the stubs java_library/java_import creation code to initialize
  the SdkLibraryToImplicitlyTrack field with the name of the creating
  module.
* Initialized the SdkLibraryToImplicitlyTrack field in the
  java_sdk_library/_import so that direct references to them will be
  tracked too.
* Added tests to verify that direct access to the .stubs child of both
  java_sdk_library and java_sdk_library_import are tracked properly.

Test: atest CtsProviderTestCases - which relies on android.test.mock
      being implicitly tracked to verify that I had not broken
	  anything. Used aapt2 dump badging to read the manifest.
	  m nothing - to run the new tests which failed before fixing the
	  code.
Bug: 156723295
Change-Id: Ia99def91e9b74d2ed0a777de04b476c00ea0393d