feat: add arithmetic function "power" with decimal type (#660)

add arithmetic function "power" with decimal type

extensions/functions_arithmetic_decimal.yaml

@@ -166,6 +166,23 @@ scalar_functions:
           - name: "n"
             value: "DECIMAL<P,0>"
         return: "DECIMAL<38,0>"
+  -
+    name: "power"
+    description: "Take the power with x as the base and y as exponent.
+    Behavior for complex number result is indicated by option complex_number_result"
+    impls:
+      - args:
+          - name: x
+            value: "DECIMAL<P1,S1>"
+          - name: y
+            value: "DECIMAL<P2,S2>"
+        options:
+          overflow:
+            values: [ SILENT, SATURATE, ERROR ]
+          complex_number_result:
+            values: [ NAN, ERROR ]
+        return: fp64
+
 aggregate_functions:
   - name: "sum"
     description: Sum a set of values.