std::vformat equivalent for hstring

[Jaiganésh Kumaran]

There only seems to be winrt::format; no winrt::vformat to specify a runtime format string.

[Charles Milette]

This is not possible because std::vformatted_size and std::vformat_to_n do not exist.

We would need a dynamically increasing temporary buffer, at which point that would be equivalent to just using std::vformat and converting to winrt::hstring after.

[Charles Milette]

This will be fixed in the future with std::runtime_format