Move NDK test modules into cc/testing.go

Move the NDK modules defined in app_test.go into cc/testing.go in
preparation for using sdk_version: "current" in more tests.

Test: all soong tests
Change-Id: I80bc31225fb4562fce42781219cefbbd6affae06

sdk/testing.go

@@ -53,6 +53,8 @@ func testSdkContext(bp string, fs map[string][]byte) (*android.TestContext, andr
 		"myapex.pk8":                                 nil,
 	}
 
+	cc.GatherRequiredFilesForTest(mockFS)
+
 	for k, v := range fs {
 		mockFS[k] = v
 	}