binary_sensor with device_class: for unavailable entities always "on-icon" is used

[ildar170975]

Every binary sensor with a specified device_class has "on-icon" & "off-icon".
But when an entity is unavailable - then currently always "on-icon" is used.
In many cases it is confusing, for instance:

Imho for unavailable entities the "off-icon" should be used.
From other side, the currently implemented logics may be considered as "this entity is unavailable, so it is of grey color; and we use an icon demonstrating a purpose of this entity" (i.e. icon is not related to the current state, it is just to demonstrate this particular device_class).

[karwosts]

I think this is implemented now.

Anyway, icons are now chosen by core. So perhaps not a frontend issue.

Example icon definition:

    "cold": {
      "default": "mdi:thermometer",
      "state": {
        "on": "mdi:snowflake"
      }
    },