Add preprocessed property for android_test_import

If set to true, preprocessed indicates that the prebuilt apk is
installable as is and does not need any further processing (e.g.
zipaligning, signing).

(This is a cherry pick.)

Test: app_test.go
Bug: 155412211
Merged-In: If0c27c1e340c1bdb270064f636dc6bf33a0fc949
Change-Id: If0c27c1e340c1bdb270064f636dc6bf33a0fc949