### Description

A query like `from employees | where true` is perfectly valid. So is `from employees | where still_hired`. In other words, a simple boolean expression is accepted, even if that expression is a field. For fields `where [field_name]` is the short version of `where [field_name] == true`.

But, for fields that are not booleans `from employees | where salary` for example, ESQL throws an exception:

```
                "type": "class_cast_exception",
                "reason": "class org.elasticsearch.compute.data.IntVectorBlock cannot be cast to class org.elasticsearch.compute.data.BooleanBlock (org.elasticsearch.compute.data.IntVectorBlock and org.elasticsearch.compute.data.BooleanBlock are in unnamed module of loader java.net.FactoryURLClassLoader @c6a692e)"
```

The error message should be more user-friendly, like validating the parameters of regular functions.
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/analysis/Verifier.java
b.set(STATS.ordinal());
            } else if (p instanceof Filter) {
                b.set(WHERE.ordinal());
            }
        });
        for (int i = b.nextSetBit(0); i >= 0; i = b.nextSetBit(i + 1)) {
            metrics.inc(FeatureMetric.values()[i]);
        }
    }
    private static Collection<Failure> validateRow(Row row) {
        List<Failure> failures = new ArrayList<>(row.fields().size());
        row.fields().forEach(a -> {
            if (EsqlDataTypes.isRepresentable(a.dataType()) == false) {
                failures.add(fail(a, "cannot use [{}] directly in a row assignment", a.child().sourceText()));
            }
        });
        return failures;
    }
    private static Collection<Failure> validateEval(Eval eval) {
        List<Failure> failures = new ArrayList<>(eval.fields().size());
        eval.fields().forEach(field -> {
            DataType dataType = field.dataType();
            if (EsqlDataTypes.isRepresentable(dataType) == false) {
                failures.add(
                    fail(field, "EVAL does not support type [{}] in expression [{}]", dataType.typeName(), field.child().sourceText())
                );
            }
        });
        return failures;
    }