The old internals reached into the global hub to stash the allocation(s)
for enum value -> string value there, then kept around a potentially
invalid (in case the hub was cleaned up) reference into it, going through
whole bunch of virtual dispatch in the process.

The new internals just store the data in a static variable inside the
`StringMaker` specialization. This avoids potential lifetime issues,
avoids all virtual dispatch and (almost) reduces the include bloat in
the main header path.

The reason for (almost) there is that for full include correctness,
`EnumInfo` needs `<utility>` include for `std::pair`. However, this brings
in things like `std::relops`, because the std headers in C++ are dumb.
As this was not included before, and instead we relied on `std::pair`
existing in an internal stdlib header that we transitively included, the
full include size ends up bigger than before.

The thread-safety changes in assertions & messages turned whether
the last assertion passed or failed into thread-local state,
instead of being member of the `RunContext`. However, this change
was not reflected in the API `CHECKED_IF`/`CHECKED_ELSE` used,
which in turn required `catch_test_macro_impl.hpp` to include
`catch_interfaces_capture.hpp` for it.

Thanks to the combination of this commit and the previous similar
commit for the message stack handling, the main include path does
not need to include `catch_interfaces_capture.hpp` anymore.

The thread-safety changes in assertions & messages turned the message
stacks into thread-local state, instead of it being member of `RunContext`.
The relevant {push,pop}(Un)ScopedMessage functions were turned from member
functions into static functions, but this left `catch_message.hpp` with
dependency on `IResultCapture`'s definition for the functions, and thus
it still had to include `catch_interfaces_capture.hpp`.

With this change, `catch_message.hpp` no longer needs
`catch_interfaces_capture.hpp`.

This has two advantages

1) Removing the include of `catch_interfaces_capture.hpp` from the
   header and potentially allowing further pruning later.
2) Providing small-but-measurable 1-2% speedup for assertions.