P3016 R6 Resolve inconsistencies in begin/end for valarray and braced initializer lists

[wg21bot]

P3016R0 Resolve inconsistencies in begin/end for valarray and braced initializer lists (Arthur O'Dwyer)

[jfbastien]

@inbal2l I'd like LEWG to consider this first, and send to EWG if needed.

[wg21bot]

P3016R1 Resolve inconsistencies in begin/end for valarray and braced initializer lists (Arthur O'Dwyer)