Doing some benchmarking with ClangBuildAnalyzer suggests that
compiling Catch2's `SelfTest` spends 10% of the time instantiating
`std::unique_ptr` for some interface types required for registering
and running tests.
The lesser compilation overhead of `Catch::Detail::unique_ptr` should
significantly reduce that time.
The compiled implementation was also changed to use the custom impl,
to avoid having to convert between using `std::unique_ptr` and
`Catch::Detail::unique_ptr`. This will likely also improve the compile
times of the implementation, but that is less important than improving
compilation times of the user's TUs with tests.
These files are not included by the default
`#include <catch2/catch_test_macros.hpp>` path, so that users do
not have to pay for them if they do not use them. Follow up is to
split out the small part of `catch_preprocessor.hpp` used by the
default test macros (AFAIK, it is just `INTERNAL_CATCH_REMOVE_PARENS`
macro), so that it is not included by the default path either.
Also fixes#1892 by providing the missing macros.
