Backport: $pad function to truncate fractional part of numeric argument

Original commit:
jsonata-js/jsonata@09dba37

Author: uw4

src/main/java/com/dashjoin/jsonata/Functions.java

@@ -561,7 +561,7 @@ public static String trim(String str) {
      * @param {string} [char] - the pad character(s); defaults to ' '
      * @returns {string} - padded string
      */
-    public static String pad(String str, Integer width, String _char) {
+    public static String pad(String str, Number _width, String _char) {
         // undefined inputs always return undefined
         if (str == null) {
             return null;
@@ -572,6 +572,7 @@ public static String pad(String str, Integer width, String _char) {
         }
 
         String result;
+        int width = _width.intValue();
 
         if (width < 0) {
             result = leftPad(str, -width, _char);