feat: build with meson by default

[jdhughes-dev]

Meson now builds every target on every platform and with every compiler that is tested, using the build file a target provides where there is one and a generated build file otherwise, so it is the default.

This changes how every target is built, so it is worth being clear about what changes.

The argument becomes --meson and --no-meson, because a build with the pymake build engine can no longer be asked for by leaving meson off. pm.meson defaults to True and can be set to False.

A meson build is always in place, and a build that is not was not, so the source of a downloaded target is no longer copied to a temporary directory before it is built by default. A target that provides a meson build file is now built with the flags that build file sets rather than the flags pymake determines, so an executable will not be identical to one built before this change.

test_build asks for the pymake build engine, which it used to get by default. Without that the pymake build engine would no longer be built or tested by anything, since test_meson_build already asks for meson.

The exclusions that kept meson from building some targets are all gone, having been a module statement meson could not read for sutra, a Windows path separator for mt3dms, vs2dt and gridgen, and the link language for mf2000, mf2005, swtv4 and mflgr.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.765%. Comparing base (44d0a28) to head (c59cfa0).

Additional details and impacted files

@@              Coverage Diff              @@
##           develop      #309       +/-   ##
=============================================
+ Coverage   79.710%   79.765%   +0.055%     
=============================================
  Files           20        20               
  Lines         3588      3588               
=============================================
+ Hits          2860      2862        +2     
+ Misses         728       726        -2     

Files with missing lines	Coverage Δ
pymake/pymake_parser.py	35.483% <ø> (ø)

... and 3 files with indirect coverage changes

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