Create new state property for vacuum which is using an enum

[gjohansson-ST]

Background

This is more or less a copy of #1140 but targets vacuum

Some entity models (like vacuum) allows integration to directly overwrite state property to set it's state using constants and are not modeled like the newer ones (as example `lawn_mower) which has a separate property for handling state using an enum.

Proposal

Similar to the lawn_mower integration implement a separate state property activity which is using an enum VacuumActivity for controlling it's state.

@final
@cached_property
def state(self) -> str | None:
    """Return the activity of the vacuum cleaner."""
    return activity

@cached_property
def activity(self) -> VacuumActivity | None:
    """Return the current vacuum entity state.

    Integrations should overwrite this or use the '_attr_activity'
    attribute to set the vacuum state using the 'VacuumActivity' enum.
    """
    return self._attr_activity

After the deprecation period integrations should only implement activity returning VacuumActivity.

Draft conceptual PR:home-assistant/core#126353

Alternatives to consider

Initial proposal was to add vacuum_state, has been updated to be modeled similar to lawn_mover using activity instead.

• Perhaps (similar to lawn_mower) the state property for a vacuum should be activity and the enum would be called VacuumActivity

Update after initial proposal

• Return the enum member instead of stringifying it's state

[MartinHjelmare]

It would be nice to make it similar to lawnmower although as for lawnmower some of the enum values don't sound as activities, eg error. Maybe not a big deal, and it's more important to leverage consistency?

[gjohansson-ST]

Same for vacuum and the state/activity is a mix of activity and state.
But I think given the two are almost the same, that we should model them similar.
There is less point in consistency between this and, as example, alarm_control_panel which is the other open proposal.
I will update the proposal.

[MartinHjelmare]

We've discussed this proposal in the Core team and decided to approve it.