Implement package_outputs in GeneralTestsOptimizer

Implement the output packaging step in the GeneralTestsOptimizer. This
step takes all the outputs built by the general-tests target (in the
case where it was optimized) and packages them into the necessary zips
generated by the target normally.

Test: atest build_test_suites_test; atest optimized_targets_test
Bug: 358215235
Change-Id: I5d27eef4e37137cc9b6e235f52f3856ba0b30460