Added device content dict to tango.sim.

[burkeds]

This dict can be imported and passed to MultiDeviceTestContext to access the demo device servers in a normal python script or ipython kernel. This step is analogous to start_ioc_subprocess used in the epics demo.

from tango.test_context import MultiDeviceTestContext
from ophyd_async.tango.sim import device_content, TangoDetector

async def test_devices():
    with MultiDeviceTestContext(device_content, process=True) as context:
        detector = TangoDetector(
            mover_trl=context.get_device_access("sim/motor/1"),
            counter_trls=[
                context.get_device_access("sim/counter/1"),
                context.get_device_access("sim/counter/2"),
            ],
            name = "detector"
        )
        await detector.connect()
        await detector.read()

await test_devices()