Interval Query should work with Annotated Text Plugin

[bijanfahimi]

Feature Request

elasticsearch version >= 7.4.2

In our use case we would like use the interval query on text fields of type annotated text. The interval query, however, throws an exception:
Can only use interval queries on text fields - not on [text] which is of type [annotated_text]"
The exception is thrown here https://github.com/elastic/elasticsearch/blob/master/server/src/main/java/org/elasticsearch/index/mapper/MappedFieldType.java#L395.

Interval query: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-intervals-query.html.
Annotated Text Plugin: https://www.elastic.co/blog/search-for-things-not-strings-with-the-annotated-text-plugin

[elasticmachine]

Pinging @elastic/es-search (:Search/Search)

[cbuescher]

Maybe @markharwood can comment on whether this field type restriction is there on purpose of if this can and should eventually be supported.