Add yield to infinite loop

[slonopotamus]

In case the loop doesn't do anything async, hub becomes unresponsive: it cannot stop program using central button, it doesn't react to stopping from the app. The only way to recover from such state is to power-cycle the hub. yield is a safety measure that ensures that hub has an opportunity to stop the program.

I've tested Mindstorms App 10.5.0 and this is what it produces for a program with empty infinite loop:

from runtime import VirtualMachine

# When program starts
async def stack_1(vm, stack):
    # Control forever
    while True:
        yield

def setup(rpc, system, stop):
    vm = VirtualMachine(rpc, system, stop, "zT3_XLSwxzq9a3X2HyM_")

    vm.register_on_start("dN8usIOJtd8aD0BgPcv-", stack_1)

    return vm

I haven't checked, but possibly other kinds of loops also need this.

[slonopotamus]

UPD: To be more exact, Mindstorms checks if there is anything async inside the loop and only inserts yield if case there isn't. This also applies to other loops (repeat <N>, repeat <until>).