Most of the changes are completely pointless renaming of constructor
arguments so that they do not use the same name as the type members,
but 🤷Closes#2015
* Added some missing `noexcept`s on custom destructors.
* Fixed `std::move` being called on a const-reference.
* Initialized `ScopedMessage::m_moved` in class definition, instead
of doing so in constructors explicitly.
* Turned some `enum`s into `enum class`es.
* Initialized `StreamingReporterBase::currentTestCaseInfo` in class
definition.
* Some cleanups in SelfTest code.
This simplified variant supports only a subset of the functionality
in `std::unique_ptr<T>`. `Catch::Detail::unique_ptr<T>` only supports
single element pointer (no array support) with default deleter.
By removing the support for custom deleters, we also avoid requiring
significant machinery to support EBO, speeding up instantiations of
`unique_ptr<T>` significantly. Catch2 also currently does not need
to support `unique_ptr<T[]>`, so that is not supported either.
