Python undocumented options about swig HOT 3 OPEN

There's a sentence about each in the output of swig -python -help, and at least some of them are documented in CHANGES (which isn't ideal but beats not being documented anywhere).

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FWIW I used to refer to #1340 all the time when I was using Python backend as this was the best source of documentation (at least a couple of years ago, maybe things have changed since then).

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That table there seems slightly terser than the descriptions in swig -python -help (which are in the manual too). The table also includes a lot of options that have since been removed.

I do wonder if some of these options are no longer helpful, as most were added a long time ago (around 2005-2006) and Python has evolved a lot since. We had a major rationalisation in 2018 which landed in SWIG 4.0.0 but it doesn't look like we actually profiled the remaining options which are intended to be optimisations.

I'd argue these options are underdocumented rather than undocumented, but there are related features which appear to actually be undocumented - e.g. the effect of -extranative can be obtained via %module(extranative="1") but I only know that from seeing that's how this feature is tested in the testsuite - being able to specify this via %module attributes doesn't appear to be mentioned in ANY documentation, not even CHANGES. Looking at where this module option is handled, there's also at least castmode and nodirprot modules options which appear to be totally undocumented (there's also a dirprot module option which only seems to be mentioned in CHANGES).

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