Add the related tests for Icon in TEST_MAPPING

It's necessary to run the following two tests if
android.graphic.drawable.Icon is modified.
* CtsGraphicsTestCases:android.graphics.drawable.cts.IconTest
* FrameworksCoreTests:android.graphics.drawable.IconTest

Test: atest -p framewroks/base/graphics/java/android/graphics/drawable
Test: cd framewroks/base/graphics/java/android/graphics/drawable; \
      atest --enable-file-patterns --collect-tests-only
Bug: 172183870
Change-Id: Ic5bcaf3231ead515aeb2cba5b7f977dbbd41f5a9