Separate android.test.mock classes from android.test.runner

The android.test.runner library contained classes in the
android.test.mock. Those classes have been extracted into a separate
android.test.mock library but are still part of the android.test.runner
library. This change removes them from the android.test.runner library.

The PackageParser change ensures that applications which specify
<uses-library android:name="android.test.runner"/> still see the same
set of classes at runtime as they did before this change.

The logic for updating the Package to maintain backwards compatibility
was extracted into its own class for a number of reasons:
* PackageParser is already huge.
* It is easier to test in separate class.
* It reduces potential for conflicts.

Bug: 30188076
Test: cts/tests/signature/runSignatureTests.sh CtsAndroidTestRunnerCurrentApiSignatureTestCases
Change-Id: I19042b3f9ffff8bf0f8437db7bb8341c703e4244

Remove android.test.mock classes from android.test.runner

Bug: 30188076
Test: cts/tests/signature/runSignatureTests.sh CtsAndroidTestRunnerCurrentApiSignatureTestCases
Change-Id: I8ddbdb0bda7bef8858202bc085881af14d7f0c92