Add repackaged legacy-test and android.test.runner

The CtsSignatureTestCases test verifies that the API described in the
api/current.txt file is actually available at runtime. The test class,
SignatureTest, requires junit and android.test classes, some from
legacy-test, some from android.test.runner which makes it impossible
(without classpath scanning) for it to verify that those classes are
accessible at runtime when they should be and inaccessible when they
should not be which is needed for the work to remove JUnit from the
Android API.

This change uses jarjar to repackage the junit and android.test classes
into repackaged.junit and repackaged.android.test packages in the
repackaged-legacy-test and repackaged.android.test.runner modules
respectively. A follow on change will switch SignatureTest over to
using the repackaged classes thus allowing it to work even when junit
and android.test classes are not visible.

Tested by making the modules and manually verifying that they contain
the classes in the repackaged package.

Bug: 35192974
Bug: 30188076
Test: see above
Change-Id: If0355a0d50b7540f416d464fdf7ffae0e4766b1c