[Enhancement] Create codegen featureset/delta documentation table

[timothytavarez]

It would make adoption more manageable for codegen if we can clearly articulate differences in compiled results. At a minimum, we should develop a documentation summary with featuresets (e.g., inheritance, metamodel differences, etc.) that can be easily grasped at a high level.

Today, language deltas are documented separately for each codegen subtarget. By putting it in a single view, we can more readily understand differences, expected results, etc.

[timothytavarez]

I'll be happy to support adding/updating this documentation.