Refactor job dependencies with needs and no change detection

What does this MR do?

In MRs: the first job for each OS is manual, then each OS proceeds independently

In main: all jobs are executed, and the needs keyword makes sure OS versions don't block each other across stages (for example release next and toolchain 13 can proceed even if base 12 is still building).

Why was this MR needed?

Because we currently attempt to do change detection, it is possible that some jobs will disappear from the pipelines. So we can't use the needs keyword to speed-up the pipeline by starting xcode builds or runner builds early. From experience, this is has a bigger toll than is gained by the few times where change detection has been able to work.

What's the best way to test this MR?

What are the relevant issue numbers?