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
if ((long) valueValues.get(0).get(1) == 1L) {
                assertEquals(20L, valueValues.get(0).get(0));
                assertEquals(2L, valueValues.get(1).get(1));
                assertEquals(20L, valueValues.get(1).get(0));
            } else if ((long) valueValues.get(0).get(1) == 2L) {
                assertEquals(20L, valueValues.get(1).get(0));
                assertEquals(1L, valueValues.get(1).get(1));
                assertEquals(20L, valueValues.get(0).get(0));
            } else {
                fail("Unexpected group value: " + valueValues.get(0).get(1));
            }
        }
    }
    
    public void testFromStatsGroupingByDate() {
        try (EsqlQueryResponse results = run("from test | stats avg(count) by time")) {
            logger.info(results);
            assertEquals(2, results.columns().size());
            assertEquals(40, getValuesList(results).size());
            
            assertEquals("avg(count)", results.columns().get(0).name());
            assertEquals("double", results.columns().get(0).type());
            assertEquals("time", results.columns().get(1).name());
            assertEquals("long", results.columns().get(1).type());
            
            List<Long> expectedValues = LongStream.range(0, 40).map(i -> epoch + i).sorted().boxed().toList();
            List<Long> actualValues = IntStream.range(0, 40)
                .mapToLong(i -> (Long) getValuesList(results).get(i).get(1))
                .sorted()