Wheel building updates

[hugovk]

Follow on from #472.

Changes proposed in this pull request:

• Now we're using manylinux2014, we can use the prebuilt manylinux2014_aarch64 image instead of building our own

• Replace archived crazy-max/ghaction-docker-buildx action with the official Docker ones

• Build each manylinux/Python combination in its own job

  • Main reason is aarch64 is slow, takes about 21 minutes in serial
  • Can still run scripts/build-manylinux-wheels.sh (locally) without specifying the Python version to build all if wanted

• Split the Windows/macOS and Linux workflows into their own files, makes the file shorter and the logic simpler, can easily diff them to see common parts, and makes it easier to build the Linux matrix

[codecov-commenter]

Codecov Report

Merging #473 (c7125ad) into main (2b13dc4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #473   +/-   ##
=======================================
  Coverage   88.96%   88.96%           
=======================================
  Files           6        6           
  Lines        1685     1685           
=======================================
  Hits         1499     1499           
  Misses        186      186           

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