Cross-call jit

If the bytecode of a call target is compiled, the jit should directly invoke it without first going through the runtime. This of course requires information like the current call stack depth to be available to the jited module.

No files, tests, or entry points are named. Start by tracing how compiled call targets currently pass through the runtime and how the JIT represents call-stack depth; the work is done when a compiled target can be invoked directly with the required state and this behavior is verified.

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