### Description

`stats x = count`  throws error `unknown column [count]` which is confusing since stats does not allow aliasing for existing columns but only points to aggregate functions.
Hence why the message should be `incorrect function declaration count, you forgot to add the parantheisis`. 
Same approach when dealing with a typo: `stats x = cont(*)` - `Unkown aggregate function cont - did you mean count()?`

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/analysis/VerifierTests.java
assertEquals(
            "1:31: first argument of [round(b)] must be [numeric], found value [b] type [keyword]",
            error("row a = 1, b = \"c\" | eval x = round(b)")
        );
        assertEquals(
            "1:31: second argument of [round(a, b)] must be [integer], found value [b] type [keyword]",
            error("row a = 1, b = \"c\" | eval x = round(a, b)")
        );
        assertEquals(
            "1:31: second argument of [round(a, 3.5)] must be [integer], found value [3.5] type [double]",
            error("row a = 1, b = \"c\" | eval x = round(a, 3.5)")
        );
        assertEquals(
            "1:9: second argument of [round(123.45, \"1\")] must be [integer], found value [\"1\"] type [keyword]",
            error("row a = round(123.45, \"1\")")
        );
    }
    public void testAggsExpressionsInStatsAggs() {
        assertEquals(
            "1:44: expected an aggregate function or group but got [salary] of type [FieldAttribute]",
            error("from test | eval z = 2 | stats x = avg(z), salary by emp_no")
        );
        assertEquals(
            "1:19: expected an aggregate function or group but got [length(first_name)] of type [Length]",
            error("from test | stats length(first_name), count(1) by first_name")
        );
        assertEquals(
            "1:19: aggregate function's field must be an attribute or literal; found [emp_no / 2] of type [Div]",
            error("from test | stats x = avg(emp_no / 2) by emp_no")
        );