chore(isthmus): minor refactoring

Author: ZorinAnton

isthmus/src/main/java/io/substrait/isthmus/SimpleExtensionToSqlOperator.java

@@ -36,7 +36,13 @@ public static List<SqlOperator> from(SimpleExtension.ExtensionCollection collect
 
   public static List<SqlOperator> from(
       SimpleExtension.ExtensionCollection collection, RelDataTypeFactory typeFactory) {
-    TypeConverter typeConverter = TypeConverter.DEFAULT;
+    return from(collection, typeFactory, TypeConverter.DEFAULT);
+  }
+
+  public static List<SqlOperator> from(
+      SimpleExtension.ExtensionCollection collection,
+      RelDataTypeFactory typeFactory,
+      TypeConverter typeConverter) {
     // TODO: add support for windows functions
     return Stream.concat(
             collection.scalarFunctions().stream(), collection.aggregateFunctions().stream())

isthmus/src/main/java/io/substrait/isthmus/sql/SubstraitSqlToCalcite.java

@@ -48,7 +48,7 @@ public static RelRoot convertQuery(String sqlStatement, Prepare.CatalogReader ca
    * @param sqlStatement a SQL statement string
    * @param catalogReader the {@link Prepare.CatalogReader} for finding tables/views referenced in
    *     the SQL statement
-   * @param operatorTable the {@link SqlOperatorTable} for dynamic operators
+   * @param operatorTable the {@link SqlOperatorTable} for controlling valid operators
    * @return a {@link RelRoot} corresponding to the given SQL statement
    * @throws SqlParseException if there is an error while parsing the SQL statement
    */
@@ -97,7 +97,7 @@ public static RelRoot convertQuery(
    * @param sqlStatements a string containing one or more SQL statements
    * @param catalogReader the {@link Prepare.CatalogReader} for finding tables/views referenced in
    *     the SQL statements
-   * @param operatorTable the {@link SqlOperatorTable} for dynamic operators
+   * @param operatorTable the {@link SqlOperatorTable} for controlling valid operators
    * @return a list of {@link RelRoot}s corresponding to the given SQL statements
    * @throws SqlParseException if there is an error while parsing the SQL statements
    */