build script: use a prebuilt VLCKit binary for compilation

This downloads the latest VLCKit binary for compiling media library. Additionally, this downloads the tools folder from vlc.git (v3 branch) to compile the build tools if no suitable binaries are detected in the current path.

This MR also adds continuous CI for this project.

This MR is marked as a draft as it depends on VLCKit!116 (merged) and therefore future binaries of VLCKit.