Add basic test coverage for sysystemfeatures-gen args

Test the following scenarios:
 * An invalid feature version is provided
 * An "android"-prefixed raw feature name is provided

In the case of the latter, any "android"-namespaced feature
must come by way of an existing PackagerManager.FEATURE_ definition.

Bug: 376463304
Test: atest systemfeatures-gen-tests
Flag: build.RELEASE_USE_SYSTEM_FEATURE_BUILD_FLAGS
Change-Id: If74899b5ebeeee7db0e9b2c8162076f8edd4381f