[3.0] package: apple: backport build script for iOS

Merged Alexandre Janniaux requested to merge alexandre-janniaux/vlc:ios-build-script-3.0/2 into 3.0.x

The build script allows building for iOS/tvOS without pulling the whole VLCKit project, to build a standalone library for integrating libvlc in applications.

The main goal is being able to maintain libVLC 3.0 without requiring the whole VLCKit environment to run tests.

Cherry-picked from master branch at commit version 44d44176 and modified the build.conf to have all enabled contribs building.

Edited by Felix Paul Kühne

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