Switch to native Spotify iOS XCFramework

[fotiDim]

Spotify have silently released an XCFramework without making a new version release on GitHub. It is just checked out in their repo. I had to change the prepare-iOS-SDK.sh script to switch to this new type of framework. In fact now it is even simpler than before.

This PR brings 2 big benefits:

• It is no more needed to manually create a module map as the XCFramework has them bundled in🎉.
• More CPU architectures are now supported. You can use the framework on iOS simulators running on Apple Silicon (ARM64e)🍏

Caveat:

• Git must be installed on dev's machine as it is needed to clone the repo in the script. We could document it in the ReadMe although Flutter requires Git so I don't think it is a real danger. Mac OS does come with Git preinstalled and Windows or Linux users cannot build iOS apps anyway.

[fotiDim]

I rebased on main and tested again on another device. I would need you to approve once more please. No changes. Everything works on my machine™️