Integration/Regression tests towards dmlc and base

Currently the only testing done is from the langserver towards langserver internals, we need to detect that the langserver works ahead-of (compatibly) or in lockstep with dmlc changes

- Check that compat feature version numbers correspond with dmlc compat feature version numbers (can be delayed until semantic analysis is in)
- Full sanity parse of all non-error-test dml files in base repo
- Some way to verify that not only do dmlc and langserver both parse, but langserver outputs semantics consistent with dmlc?

This will involve checking out the dmlc and/or the full base repo/package during the test and running towards those files. Probably also needs to run the cmake dependency stage for the dependency info.