* Use CMD as the shell and simplify configure/build steps
* Include plaform in the build name

For now I added only the basic build matrix, without coverage
collection and more special builds, like WMAIN.

However, due to GHA being so much faster than AppVeyor, all
these builds are now done against the 'all-tests' prefix, making
the builds more uniform than they were on AppVeyor.

Also adds a CI job for Bazel build to avoid future breakage.

* Add missing files to `tests/meson.build`
* Rename meson build workflows to be more easily identifiable

The Meson[1] build system makes it easier incorporate third-party
libaries into a project if they also build using Meson.

Let's add a minimal Meson build that's compatible with the CMake build,
along with a GitHub workflow to check that it builds and that at least
the simplest SelfTest runs.

The handling of catch_user_config.hpp is inspired by BUILD.bazel and
doesn't attempt to support any configuratons options. Such features
could be added later.

Meson strongly discourages using wildcards to specify sources, so the
source and header lists are copied from CMakeLists.txt.

Add a new test workflow to test the Meson builds. I was unable to get
these tests to pass with Ubuntu 20.04, so they use Ubuntu 22.04.

I'm neither a CMake nor a Meson expert, but the results seem to work for
me.

[1] https://mesonbuild.com/

Co-authored-by: Mike Crowe <mcrowe@brightsign.biz>

Also updated GCC version to GCC-11, which is packaged in the
runner image.