[ios] Use build script for libcrypto

[paw-hub]

Set up a submodule that tracks external build tools, and have a script automatically compile libcrypto for iOS Simulator (arm64/x86_64) and iOS (arm64).

Stop tracking the libcrypto binary in git.

Also stop using a .xcframework and just conditionally static-link the .a files depending on architecture, and use the include directory from the build tools.

Fixes #6603

[paw-hub]

Still some remaining questions:

• Figure out a good way to avoid committing binaries?
• The filename is OpenSSL.xcframework, not libcrypto.xcframework, but libssl.a was removed prior to creating this file, so it's not actually a part of the final archive. That said, the script for making the xcframework only seems to result in a OpenSSL.xcframework file. Is this OK?

[paw-hub]

This seems to work well enough now that it can be reviewed.

That said, on our Mac Mini with Apple Silicon, initial builds take around 78 seconds longer due to having to compile OpenSSL three times (iOS on arm64 and iOS-Simulator on arm64/x86_64).

This isn't an issue for developers, since it only has to do this task once and subsequent builds are instant, but for making releases, is this an issue? Release builds already take a while, so it's not that much longer (relatively). We can probably improve this with some sort of caching (as @rezbyte suggested) if it's worth it.

[charlag]

We can tell the builder to not wipe the repo if that helps. I think this isn't a bit issue

[charlag]

We probably need some test notes

[paw-hub]

Closed because we're removing libcrypto via #7344