Implement get_item_defs() client-side call

[appgurueu]

Logical extension of get_item_def, another #10003 split-off.

[sfan5]

Do you plan to make another PR for get_node_defs .. or?

[paramat]

👎 I do not like doing this, but i disapprove because i think CSM features should not be accepted until SSCSM is implemented.
This also comes with an apology because we are not clear about the acceptance of CSM contributions and about our approach to the CSM situation, we are inconsistent. I am attempting to put this right in #10530 by getting an official decision.

[Zughy]

@appgurueu are you gonna continue with this? "Action / change needed" label, will close in 10 days if I receive no answer

[appgurueu]

This is now in a mergeable state. Adding get_node_defs() would require more work (in particular exposing a list of all nodenames, which the NodeDefManager doesn't do).

[appgurueu]

Closing this because CSMs seem to be a dead end anyways so far (and I will reimplement my online craftguide without requiring clients to render items). Not to mention that this should probably use a shared table to be accessed by all CSM (which would raise the question of how to protect it from writes).