CWG2697 Deduction guides using abbreviated function syntax

[jensmaurer]

It is unclear whether deduction guides are intended to be expressible using abbreviated function syntax.

See CWG2697 for details.

CWG solicits EWG design guidance in that matter.

[erichkeane]

EWG discussed this during the May 11th, 2023 telecon, and the following poll was taken:

For CWG2697, CWG should clarify that Abbreviated Function Syntax should not be permitted in deduction guides (without prejudice against a future proposal to give concrete meaning to this syntax).

SF	F	N	A	SA
4	6	2	0	0

Result: Consensus

This should provide sufficient feedback for CWG to clarify our intent, so reassigning to CWG.