Deterministic rake swig

[jacobvosmaer]

When I run rake swig on my development machine it is easy to get unwanted changes in the _wrap.cxx files. It would be nice if rake swig was deterministic. It makes life easier for contributors, and we could also check in CI that the generated files checked into Git are "correct".

Some things we would have to fix:

• pin a version of taglib to run swig against. we could make a script that downloads a specific taglib tarball and unpacks it locally
• run sed after swig to fix the @SWIG comments to use a fixed path (we can use swig -swiglib to find the string that needs to be replaced)
• check the swig version from within rake swig
• ... anything else ?

[robinst]

Sounds good!

• We already have some logic to download and use a specific version of taglib/swig in CI, can we move that out of there and into rake or a script? If not that's fine, maybe it's too different.
• Yes, looks like we need sed. I've opened an issue about this with swig a long time ago: Generated wrappers include path to SWIG installation in macro comments swig/swig#202

[jacobvosmaer]

OK! I can work on this.

[robinst]

Nice! Can you base it on main? We can later merge it into the taglib-2 branch (or rebase).