Fixes the inconsistency between the type of the object returned by the
`SIGN()/SIGNUM()` SQL functions and the specified `DataType`.
In the Class Sign, DataType is DataTypes.INTEGER. The source code is as
follows：
```
public DataType dataType() {
return DataTypes.INTEGER;
}
```
But In the Class MathProcessor, the source code of SIGN((Object l),
Parameter and return value types are the same. Therefore, when using
double or float parameters to test, there is a little problem, the test
method is like the following curl :
```
curl -XPOST 127.0.0.1:9200/_sql -d "{\"query\":\"select SIGN(1.0) \"}" \
-H 'Content-Type: application/json'
```
The result is:
```
{"columns":[{"name":"SIGN(1.0)","type":"integer"}],"rows":[[1.0]]}
```
The result value is `1.0`, but the type is `integer`.
Signed-off-by: mantuliu <240951888@qq.com>
Co-authored-by: Marios Trivyzas <matriv@gmail.com>
(cherry picked from commits aa78301e71f, ced3c1281c7, 40e5b9b)
a7301065d7