Separate headers for "extra" std types

**Description**
Currently, to add stringification for std::optional, say, you need to define `CATCH_CONFIG_ENABLE_OPTIONAL_STRINGMAKER`. This can be tricky to get right with things like pre-compiled headers, unity builds, or other tricks to speed up the build, without dragging it into every single unit test file in the project.

Given Catch2v3 has already gone down the route of using separate headers for extra functionality, it would be useful to have this option here as well - put the relevant StringMaker specialisations into their own headers. That way, enabling formatted output of these types would just involve adding an extra #include, and it would work just fine with PCH, unity builds, etc.

Start by inspecting Catch2 v3's existing separate headers for extra functionality and locating the StringMaker specialisations for std::optional and other extra standard types. Determine how those headers are included and how the current configuration macro is used. Done means formatted output for these types can be enabled through additional includes without requiring the macro in every unit test file.

Written by the indexing model from the issue text.