Moves runTestWithSnapshots to receive a TestScope instead of a Kosmos.

- Placed in a new compose package under tests/utils so it's not
  perceived as part of the Kosmos package
- Kosmos.runTest automatically uses this as well so nobody has to worry
  about it
- Converts existing usages to Kosmos.runTest

Bug: 387321113
Flag: TEST_ONLY
Test: irrelevant
Change-Id: I8d8f621d303ab422258fef62dfee94c32f95c3cd