This commits also adds a script that does the amalgamation of headers
and .cpp files into the distributable version, removes the old
`generateSingleHeader` script, and also adds a very simple compilation
test for the amalgamated distribution.

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 :shrug:

Closes #2015

The base was also renamed from `TestEventListenerBase` to
`EventListenerBase`, and modified to derive directly from the
reporter interface, rather than deriving from `StreamingReporterBase`.

Each of the two reporter bases now has its own header file, and
cpp file. Even though this adds another TU to the compilation,
the total CPU time taken by compilation is reduced by about 1%
for debug build and ~0.5% for optimized build of the main library.
(The improvement would be roughly doubles without splitting the TUs,
but the maintainability hit is not worth it.)

The code size of the static library build has also somewhat decreased.

Follow up: Introduce combined TU for reporters, and further split
apart the catch_reporter_streaming_base.hpp header into its
constituent parts, as it still contains a whole bunch of other stuff.

* 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.