Have meson codesign binaries/dylibs for macOS

[StarWitch]

When developing locally on macOS, you'll run into errors like this if you try to do a meson install -C build/ and run the resulting Taisei.app:

$ ./Taisei 
dyld[91792]: Library not loaded: @executable_path/dylibs/libcrypto.3.dylib
  Referenced from: <EFAC9454-72D8-387F-B0C4-2E852F1F7DE7> /Users/username/Applications/Taisei.app/Contents/MacOS/Taisei
  Reason: tried: '/Users/username/Applications/Taisei.app/Contents/MacOS/dylibs/libcrypto.3.dylib' (code signature in <45FFB471-EF30-33DC-8172-4F545AC88544> '/Users/username/Applications/Taisei.app/Contents/MacOS/dylibs/libcrypto.3.dylib' not valid for use in process: Trying to load an unsigned library)
[1]    91792 abort      ./Taisei

This can be solved by running codesign -s - on the dylibs that meson pulls into the build.

An example of how to do this in meson can be found here: link