Test `CMake` build system support in `GitHub Actions`

[hummeltech]

This pull request depends on #284

• Added macOS building & testing
• Added FreeBSD building & testing
• Added new Linux distributions for building & testing
  • almalinux:8 (Released 2021-03-30)
  • amazonlinux:2 (Released @ 2018)
  • debian:testing (TBA)
  • fedora:35 (Released 2021-11-02)
  • fedora:36 (Released 2022-05-10)
  • fedora:rawhide (Released @ 2022-10-18)
  • rockylinux:8 (Released 2021-06-21)
  • ubuntu:22.04 (Released 2022-04-21)
• Removed EOLed Linux distributions for building & testing
  • fedora:33 (EOLed 2021-12-01)
  • fedora:34 (EOLed 2022-06-01)
• The existing Autotools build system will still be tested on Ubuntu 22.04 & macOS 12
• Coverage is enabled for CMake/GNU testing on Ubuntu 22.04
• LLVM (clang) building & testing is enabled on FreeBSD, macOS & Ubuntu 22.04

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Here's an example of building & testing when on the master branch (or on develop).

[pantierra]

This is great. We need some testing, and then I am all in favour of bringing this in.

[pantierra]

In order to keep things simple and not to stress to much on the build-resources, I would prefer not to include the following builds:

• almalinux
• amazonlinux
• rockylinux

Totally love that you are updating the version of the existing ones (Fedora, Ubuntu, and Debian) and include FreeBSD and macOS.

[hummeltech]

@xamanu Sure thing, I removed them from the build matrix!

[hummeltech]

Alright @xamanu, I think this is ready too. I've also created a Docker-based build pipeline that can also be used to test/demonstrate locally. I would like to follow this up with a docs update as well.

[pantierra]

Great. Please reroll with latest master which includes the cmake build system.

[hummeltech]

Alright @xamanu, this should be ready for review now. I needed to make a few minor changes to the CMake configuration to allow for building mod_tile with Mapnik >= 4 using CMake.