Track Deprecations #4159
Description
We should track any existing deprecations in Rakudo noting: which version it's deprecated in, and which version it will be removed in.
This can be done by pulling from the rakudo source (to start), and we need to decide where to keep this info. Should appear in the docs next to each feature (once removed, we can mark it as removed as of version X). If we have a clean way to annotate this in POD, we don't need a summary page, we can just grep the source to get a listing. (Users will care more about individual deprecations in situ rather than a full listing)