ESQL: Add url_decode function (elastic#133494)

Author: mouhc1ne

x-pack/plugin/esql/qa/testFixtures/src/main/resources/string.csv-spec

@@ -2623,3 +2623,37 @@ ROW u = "%21%23%24%26%27%28%29*%2B%2C%2F%3A%3B%3D%3F%40%5B%5D" | EVAL u = URL_DE
 u:keyword
 "!#$&'()*+,/:;=?@[]"
 ;
+
+combined url encode decode tests with table reads
+required_capability: url_encode
+required_capability: url_decode
+
+FROM employees 
+| SORT emp_no
+| LIMIT 10
+| EVAL name = URL_DECODE(URL_ENCODE(CONCAT(gender, " - ", first_name, "+", last_name, "; ", CONCAT("@", first_name, last_name))))
+| KEEP emp_no, name;
+
+emp_no:integer | name:keyword
+10001          | M - Georgi+Facello; @GeorgiFacello
+10002          | F - Bezalel+Simmel; @BezalelSimmel
+10003          | M - Parto+Bamford; @PartoBamford
+10004          | M - Chirstian+Koblick; @ChirstianKoblick
+10005          | M - Kyoichi+Maliniak; @KyoichiMaliniak
+10006          | F - Anneke+Preusig; @AnnekePreusig
+10007          | F - Tzvetan+Zielinski; @TzvetanZielinski
+10008          | M - Saniya+Kalloufi; @SaniyaKalloufi
+10009          | F - Sumant+Peac; @SumantPeac
+10010          | null
+;
+
+combined url encode decode tests with random strings
+required_capability: url_encode
+required_capability: url_decode
+
+ROW u = ["https://www.example.com/papers?q=information+retrieval&year=2024&citations=high", "", "!#$&'()+/:;=?@[]", "💨🔥🪨💧"] 
+| eval u = URL_DECODE(URL_ENCODE(u));
+
+u:keyword
+["https://www.example.com/papers?q=information+retrieval&year=2024&citations=high", "", "!#$&'()+/:;=?@[]", "💨🔥🪨💧"]
+;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/scalar/convert/UrlDecode.java

@@ -87,9 +87,6 @@ public EvalOperator.ExpressionEvaluator.Factory toEvaluator(ToEvaluator toEvalua
     static BytesRef process(final BytesRef val) {
         String input = val.utf8ToString();
         String decoded = URLDecoder.decode(input, StandardCharsets.UTF_8);
-
-        // System.out.println(String.format("in: %s - out: %s", input, decoded));
-
         return new BytesRef(decoded);
     }
 }