Add `doc(plugins)`, `doc(passes)`, etc. to INVALID_DOC_ATTRIBUTES

[camelid]

I think we should make doc(plugins), doc(passes), and any similar attributes hard errors. doc(plugins) is a no-op, and I expect there are almost no people using it. I'm not sure about the status of doc(passes), but I think it's been deprecated for several years. There are probably other similar attributes that should become hard errors, so please comment if you know of more.

I'm not sure if we need to wait to do this in the 2021 Edition since these attributes are likely not used at all, but I'm tagging this issue as lang-team-202x-edition and will note this in the #edition 2021 Zulip stream in case it has to happen across an edition boundary.

cc #82651, #44136
cc @rust-lang/rustdoc

[jyn514]

I think this should be part of INVALID_DOC_ATTRIBUTES and be treated the same way as all those future-deprecation warnings. I don't think they need to be special-cased to give hard errors when nothing else does.

[jyn514]

doc(passes) is a weird one because it does still work. I don't think we should make it an error.

[camelid]

I don't think we should make it an error.

You don't think we should make it a hard error or you don't think we should make it deny-by-default?

[camelid]

Also, I thought doc(passes) was deprecated, but I don't get any errors or warnings on nightly.

[jyn514]

I don't think we should make it an error.

You don't think we should make it a hard error or you don't think we should make it deny-by-default?

I don't think it should be made an error (either kind). Deprecating it seems ok though.

[Manishearth]

We should just include them in INVALID_DOC_ATTRIBUTES. No hard errors without going through future incompat machinery or editions please.