This enables building with NumPy on Linux and macOS. Windows support
should be complete to, but is untested as of now and may need a few
tweaks. This contains:
- A set of `meson.build` files and related code generation script
tweaks, header templates, etc.
- One CI job on Linux
- Basic docs on using Meson to build NumPy (not yet integrated in the
html docs, it's too early for that - this is for early adopters right
now).
The build should be complete, with the major exception of SIMD support.
The full test suite passes. See gh-22546 for the tracking issue with
detailed notes on the plan for switching NumPy to Meson as its build
system.
Co-authored-by: Stefan van der Walt <stefanv@berkeley.edu>