Fix GET_FORMAT UDF (#3543)

by adding Locale.ROOT when converting string to lowercase to avoid irregular casting of I when defaulting to Turkic languages

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

core/src/main/java/org/opensearch/sql/expression/datetime/DateTimeFunctions.java

@@ -1510,10 +1510,12 @@ public static ExprValue exprFromUnixTimeFormat(ExprValue time, ExprValue format)
    */
   public static ExprValue exprGetFormat(ExprValue type, ExprValue format) {
     if (formats.contains(
-        type.stringValue().toLowerCase(), format.stringValue().toLowerCase(Locale.ROOT))) {
+        type.stringValue().toLowerCase(Locale.ROOT),
+        format.stringValue().toLowerCase(Locale.ROOT))) {
       return new ExprStringValue(
           formats.get(
-              type.stringValue().toLowerCase(), format.stringValue().toLowerCase(Locale.ROOT)));
+              type.stringValue().toLowerCase(Locale.ROOT),
+              format.stringValue().toLowerCase(Locale.ROOT)));
     }
 
     return ExprNullValue.of();