Make the necessary changes for the code base to compile with JDK 21.
Other changes:
1. Upgraded testcontainer version and the SQL image version (to be the
same as what we use in Cloud SQL). This led to some schema changes and
also changed the order of results in some test queries (for the
better I think, as the new order appears to be alphabetical).
2. Remove dependency on Truth8, which is deprecated.
3. Enable parallel Gradle task execution and greatly increased the
number of parallel tests in standardTest. Removed outcastTest.
