[Feature Request] Make helper function is_exposed() more available

[jleinenbach]

To reduce tokens, I do not publish all entities in my first prompt. I would like to be able to filter non-exposed entities, similar to the HA function "is_hidden_entity()" Please make the helper function is_exposed() more available, not just for sqlite.

This is my non-elegant workaround as sqlite includes this function:

...
        response_variable: filtered_entity_ids
      - type: sqlite
        query: >-
          {% set ns = namespace(exposed_entities = '') %}
          {% set entity_ids = (filtered_entity_ids | from_json) %}

          {% for entity_id in entity_ids %}
            {% if is_exposed(entity_id) %}
              {% set ns.exposed_entities = ns.exposed_entities + entity_id + ',' %}
            {% endif %}
          {% endfor %}
          {% if ns.exposed_entities %}
            SELECT '{{ ns.exposed_entities[:-1] }}' AS result;
          {% else %}
            SELECT '' AS result;
          {% endif %}
        response_variable: result
      - type: template
        value_template: >-
          {% if result is defined %}
            {% set json_result = result | tojson %}
            {% set result_value = (json_result | from_json)[0].result | default('', true) | safe %}
          {% else %}
            {% set result_value = '' %}
          {% endif %}
...