Test script for source tree treble build

The script tests building two targets with a sigle build artifact
path.
Give two targets A and B, build A and then build B without cleaning
the out directory. After that, build the A again.

Bug: 284915566
Test: combined_build_test.sh -t cf_x86_64_phone \
             -a cf_x86_64_foldable -v userdebug -c -d out/dist droid
Change-Id: I143412ca67717a5ee3b437c84b230a58a00b065e
1 file changed