MODE-2272 Java Sequencer Should Be Thread-Safe

The JavaFileSequencer was holding state in a field referencing the source file recorder. I removed that field and now the sequencer creates a new JdtRecorder each time JavaFileSequencer.execute is called. Also removed some constants and a method that was not being used. Test case also added. However, on rare occasions, running the test case in Eclipse still throws the NodeNotFoundInParentExceptiondocumented in the issue.