Test using soong_config_module_type with singleton module type

Singleton module types have some special behavior that can cause
problems when trying to extend them with soong_config_module_type so
this adds some tests of how they work together.

Currently, the tests show that they do not work together, a follow up
change will correct that.

Bug: 264876909
Test: m nothing
Change-Id: I250ee4e18b3c04d1c91808f55722da74b813a570