Improve test-vector format to handle syscalls

[ZenGround0]

Most scenario test messages generate test vectors that cannot be used for scenario testing because scenario tests fake syscall implementations and the current test-vector format cannot handle this, instead relying on a complete syscall implementation.

We should modify the test-vector format so that conformance test drivers can take advantage of a syscall input->output mapping directly specified in the vector.

When we do this the vm fakeSyscallsAccessed boolean can be removed as the generated conformance test vector corpus will be all generated vectors instead of the current subset not calling syscalls.