Parse and convert the synthetic flag of java methods

[thomasspriggs]

For use in a downstream repository. This is used to indicate whether a
method was synthesized by the java compiler, as opposed to being a
method which has corresponding user written java code.

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[smowton]

One typo to fix

[smowton]

not be