Base SL4A+SL4A test

Implement base test for SL4A+SL4A combination testing.

First test is WIP so not included in this CL and will be added in a
follow-on CL.

Test: gd/cert/run --device --clean --sl4a_sl4a [test_name]
Bug: 222349537
Change-Id: Id9eebe0745ea8e516f1d47c6a0e71b14786c7f3e