javascript: rename and simplify DB.callInTransaction() as DB.transaction(). Add DB...

javascript: rename and simplify DB.callInTransaction() as DB.transaction(). Add DB.savepoint(), which works the same as transaction() but uses savepoints. Correct concatenation of arguments to SQLite3Error to use spaces instead of commas. Test that demo-oo1.js works with persistent OPFS storage (output differs due to persistent rows, but the demo works).

FossilOrigin-Name: e8c323f12b6223bc9dcbbec40698969c7917128aa50cf599c247df23f607ae61