Migrate build backend from setuptools to mesonpy (meson-python)

[mwtoews]

As noted here, many Python projects that have compiled objects have been steady shifting from setuptools to meson-python (docs). As version 2.0 is in early in the development cycle, now is a great time to consider migrating Fiona's build backend in a similar fashion.

[sgillies]

@mwtoews one thing I hadn't noticed until now is that meson-python is version 0.16.0. Which implies to me an unfinished state and future breaking changes. And I see a lot of unresolved discussions in the project. Distutils/setuptools isn't great, but at least it is "done". Our workarounds for missing features should continue to work for the foreseeable future.