* add support for fallback_formatter in detail::write
* add ToString test into OStreamTest
to check fmt::to_string() with class that has output stream operator
* add WithOstreamOperator test into CompileTest
to check fmt::format() with FMT_COMPILE() and class that has output stream operator
* use conditional_t inside detail::write instead of 2 overloads
* Revert "add WithOstreamOperator test into CompileTest"
* remove Context from template parameters in detail::write
1651b2d433