Removed arguments from JSScriptEngine.getInstance() singleton factory method.

Also made some minor changes / refactorings while at it:

- Removed redundant "throws Exception1, Exception2, Exception3" from tests
- Removed redundant @NonNull
- Made classes that shouldn't be extended final
- Added missing test case
- Implemented toString() on Profiler and LoggerFactory.Logger

Test: atest AdServicesJsEngineUnitTests AdServicesServiceCoreProtectedAudienceUnitTests:JSScriptEngineE2ETest

Bug: 365833970
Bug: 366228321
Flag: EXEMPT (bug 337358613)
Change-Id: I3903ab04f0d0d66bda6ca3a2f59e8dc337af5403
13 files changed