Support 'deprecated' as an Alias for 'deprecate'

[InsertCreativityHere]

This PR implements #2093. After I centralized all the deprecation checking to the Parser, only these 2 functions need to be changed.

Let me know if the logic for isDeprecated is too hacky. Honestly, I'm pretty sure it is...

[externl]

Definitely a bit hacky (the original lookup). Should we fix this code to be a bit better?

[InsertCreativityHere]

It was on the edge of being too hacky for me, so I'll unhackify it, even if it's a little redundant.

If we ever add proper metadata validation in the future, it'd probably break this code as-written.