P3548 R0 P1030 `std::filesystem::path_view` forward progress options

[wg21bot]

P3548R0 P1030 std::filesystem::path_view forward progress options (Niall Douglas)

[inbal2l]

This paper is the outcome of the Wroclaw discussion on P2645, P1030 (see here) and proposes options to resolve concerns.

[tahonermann]

SG16 should review this paper along with #2056 (P2645R1: path_view: a design that took a wrong turn ); adding the sg16 label.