De-fatalize calling undefined import/unimport method with arguments

[ap]

The merge of #23992 caused too much fallout: #24013

We discussed this in PSC meeting #210 yesterday and decided that the deprecation be rescinded and that #23992 effectively be reverted. We want this mistake to only warn, as it did before, but with an appropriate warning category so that whoever wants the error can opt into it.

Ideally this won’t be a revert but a new patch; e.g. the doc patches mostly shouldn’t be reverted per se, since they would reintroduce the language about this being deprecated. They need to be edited to align with the new decision instead, along with any other POD and whatnot that declares this deprecation or mentions that this is to become an error, etc. Plus of course we need the warning to have a category.

[haarg]

Should these warnings be enabled by default?

[ap]

Should these warnings be enabled by default?

IMO, given that it catches real mistakes, yes. We’ll see whether that still causes unacceptable fallout and may adjust accordingly, but for now, let’s go with yes.