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.
although it's good to have the test in the codebase for regression, this is not only very much timing dependent, but also it takes a bit of times to run based on the iteration count. So IMO this should be `@Ignored`