iOS Example: Fix the build to make it work again

[badboy]

This includes:

• Correctly calling uniffi-bindgen through cargo.
• Ditching lipo for individual static libraries per target, that way it easily works on all Mac hardware (x86_64 or arm64) as well as for iOS hardware targets.
• Build a staticlib using cargo's new --crate-type option

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Replaces #1436.
This wills locally on my M1 macbook using Xcode 14.2 and rustc 1.65.0

[mhammond]

This looks fine to me, but it is still "broken" due to https://github.com/mozilla/uniffi-rs/blob/main/rust-toolchain.toml forcing me on 1.63 - should we bump that first? (Or soon, I don't really care)

(I was going to suggest a change there might be to note "rustup override ..." in README.md for that example, but that looks quite stale or confused, so 🤷 )

[badboy]

This looks fine to me, but it is still "broken" due to main/rust-toolchain.toml forcing me on 1.63 - should we bump that first? (Or soon, I don't really care)

D'oh! yeah, i've been testing with stable locally here of course. --crate-type was stabilized in 1.64.0. We should just upgrade. I'll do that.

(I was going to suggest a change there might be to note "rustup override ..." in README.md for that example, but that looks quite stale or confused, so 🤷 )

Of course I forgot to even look at the README. I'll also update that (as well as the book).