Add extra notes to ranges::c* to mirror ranges::*

[strega-nil-ms]

Given the new changes to cbegin and friends from P2278R4, where they are no longer simple wrappers around begin and friends, it is (in my opinion) confusing that they lack a similar note about how "ill-formed means substitution failure".

[tkoeppe]

What about ranges::ssize?

Is the reason that we don't have notes here that the items in question are "expression-equivalent" to one of the items with notes, and those those notes apply transitively?

[CaseyCarter]

Is the reason that we don't have notes here that the items in question are "expression-equivalent" to one of the items with notes, and those notes apply transitively?

Roughly. The notes (which should maybe be normative) are to clarify the cases where the wording explicitly says "cpo_expression(meow) is ill-formed". It's "clear enough" that "cpo_expression(meow) is expression-equivalent to other_expression" implies that cpo_expression(meow) is ill-formed in the immediate context of a template instantiation when and if other_expression is, but e.g. "If T is an array of unknown bound, ranges::empty(E) is ill-formed." could mean any kind of ill-formed.

[CaseyCarter]

I suppose by my argument, "If ranges::size(t) is ill-formed, ranges::ssize(E) is ill-formed." requires a note. Shout if you'd like me to add one in a separate PR (strega-nil-ms probably has better things to do).

[tkoeppe]

Do the notes describe a consequence of existing specification, or state a novel requirement?

[jwakely]

Do the notes describe a consequence of existing specification, or state a novel requirement?

That has been the subject of some debate.