Enumerate nested devices in plan schemas

[callumforrester]

Following #526 plan schemas include enums of all possible devices that can be supplied, for example:

{
  "bump_motor": {
    "additionalProperties": false,
    "description": "",
    "properties": {
      "motor": {
        "description": "",
        "enum": [
          "x",
          "y"
        ],
        "title": "Motor",
        "type": "bluesky.protocols.Movable"
      }
    }
  }
}

However, if devices are nested they are not picked up by this process, so if I have

class SimStage(StandardReadable):
    def __init__(self, name: str = "") -> None:
        with self.add_children_as_readables():
            self.x = Motor("BAZ:")
            self.y = Motor("BLARG:")
        super().__init__(name)

It does not appear, I would expect something like

{
  "bump_motor": {
    "additionalProperties": false,
    "description": "",
    "properties": {
      "motor": {
        "description": "",
        "enum": [
          "sim_stage.x",
          "sim_stage.y"
        ],
        "title": "Motor",
        "type": "bluesky.protocols.Movable"
      }
    }
  }
}

I have created a failing test in #1127

Acceptance Criteria

• Nested devices are included in enums
• Failing test linked above passes

[callumforrester]

JW: Relates to #903, if we had all of the child devices registered then both of these would come for free

Some discussion about names of children and referencing them with "parent-child" (the name) vs. "parent.child" which blueapi allows you to use to reference a device because it splits on strings. If we register all of these children, should we support getting them by name or by their dotted access?

We will support the named access "parent-child" for all of the devices that are registered. For now we continue to support "parent.child" as removing support is breaking #1137. When wanting to run a plan that uses stage-x and stage-y, write the plan to take stage: else, all Motors are exposed in a flat list.