CWG2600 [expr.new] p2 should cover placeholder for a deduced class type

[xmh0511]

Full name of submitter (unless configured in github; will be published with the issue): Jim X

[expr.new] p2 says

If a placeholder type appears in the type-specifier-seq of a new-type-id or type-id of a new-expression, the allocated type is deduced as follows: Let init be the new-initializer, if any, and T be the new-type-id or type-id of the new-expression, then the allocated type is the type deduced for the variable x in the invented declaration ([dcl.spec.auto]):

The cross-reference to placeholder type that only refers to [dcl.spec.auto], however, according to the example after the rule, a placeholder for a deduced class type should be also covered by this rule.

[dcl.spec.auto.general] p1 explicitly says

A placeholder-type-specifier designates a placeholder type that will be replaced later by deduction from an initializer.

However, [dcl.type.class.deduct] does not say a placeholder for a deduced class type designates a placeholder type.

[jensmaurer]

I've made that a drive-by fix in the suggested resolution for CWG2600.