The ES|QL `COUNT_DISTINCT` function fails with an `illegal agg type: text` error when it's run on a `text` field. It's fine with `keyword` fields. Compare to for example `COUNT`, which runs fine on text fields:

```
PUT test/_doc/1
{
  "foo": "bar"
}

# This fails with illegal agg type: text:
POST /_query
{
  "query": """
    FROM test
    | STATS count = COUNT_DISTINCT(foo)
  """
}

# This works:
POST /_query
{
  "query": """
    FROM test
    | STATS count = COUNT_DISTINCT(foo.keyword)
  """
}

# COUNT is fine with text fields:
POST /_query
{
  "query": """
    FROM test
    | STATS count = COUNT(foo)
  """
}
```

Full error message:

```
{
  "error": {
    "root_cause": [
      {
        "type": "esql_illegal_argument_exception",
        "reason": "illegal agg type: text"
      }
    ],
    "type": "esql_illegal_argument_exception",
    "reason": "illegal agg type: text"
  },
  "status": 500
}
```
x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/EsqlActionIT.java
}
    }
    public void testUngroupedCountAll() {
        try (EsqlQueryResponse results = run("from test | stats count(*)")) {
            logger.info(results);
            assertEquals(1, results.columns().size());
            assertEquals(1, getValuesList(results).size());
            assertEquals("count(*)", results.columns().get(0).name());
            assertEquals("long", results.columns().get(0).type());
            var values = getValuesList(results).get(0);
            assertEquals(1, values.size());
            assertEquals(40, (long) values.get(0));
        }
    }
    public void testUngroupedCountAllWithFilter() {
        try (EsqlQueryResponse results = run("from test | where data > 1 | stats count(*)")) {
            logger.info(results);
            assertEquals(1, results.columns().size());
            assertEquals(1, getValuesList(results).size());
            assertEquals("count(*)", results.columns().get(0).name());
            assertEquals("long", results.columns().get(0).type());
            var values = getValuesList(results).get(0);
            assertEquals(1, values.size());
            assertEquals(20, (long) values.get(0));
        }
    }
    public void testGroupedCountAllWithFilter() {
        try (EsqlQueryResponse results = run("from test | where data > 1 | stats count(*) by data | sort data")) {
            logger.info(results);
            assertEquals(2, results.columns().size());