Disable range formatter when user provides one

[Arghnews]

Disable formatting type as range if user provided format_as function exists, using that instead. Should fix issue raised in #3839 by @drouhard

Edit: ah, this will need a similar workaround to detail::is_formattable_delayed for old msvc versions, before it will pass all the CI tests

[vitaut]

Thanks for the PR but I don't think this will work for formatter specializations and having this just for format_as would be inconsistent. fmt::format and std::format already have an opt out mechanism for ranges.

[jdrouhard]

What is the opt-out mechanism for a type if I don't want to include <fmt/ranges.h> in the header where the type is defined?

[vitaut]

You could probably forward declare is_range but I would recommend including <fmt/ranges.h> since you are effectively defining formatting for ranges.