Test new "when" directive

[svonworl]

This PR tests mr-c's "when" implementation, https://github.com/galaxyproject/gxformat2/pull/74/commits, which I merged with master of https://github.com/galaxyproject/gxformat2. I imported the resulting source into this repo (which incorporates denis-yuen's recent binding updates) via updateparser.sh , added a dependency to the pom to get it building, and modified the appropriate IT to point at a forked test repo that incorporates a "when" clause in a galaxy format 2 file. The test repo is currently in my github account, we can move it if necessary.

This code builds, the tests pass, and I was able to load the resulting Galaxy plugin into a develop build of Dockstore and successfully import a Galaxy repo containing two versions: one with a well-formed "when" directive, which Dockstore marks valid, and one with a not-well-formed "when" directive, which Dockstore marks not valid. Dockstore displays a validation error message when I view the latter sourcefile.

The ITs don't currently contain a test for a bad "when" directive (for example, a "when" in the right position, but with malformed value), but I did try to load one while creating the test repo (when: true rather than when: "true"), and the IT failed correctly.

So, tentatively, I think it all works!

[denis-yuen]

Yeah, I think this makes sense and is what I expected.

[denis-yuen]

Approving, but not in the sense of approving for merge(?)
This is a bit weird, we should tag the CWL/Galaxy folks to let them know we looked into this albeit with a big lag.