incompatible_disable_objc_library_transition

[comius]

• Removes a transition from objc_library
• Needs migration when objc_library is built for the wrong platform directly

[keith]

I've submitted #20082 to flip this on 7.x, is that reasonable?

Also I haven't touched the j2objc_library rule. In order to entirely remove the transition from bazel we'd have to remove it from that rule as well, is that feasible at google? Or is that rule going to need it indefinitely