Revert-mistaken remove concat method. And add test-case

Author: momosetkn

doma-kotlin/src/main/kotlin/org/seasar/doma/kotlin/jdbc/criteria/expression/KExpressions.kt

@@ -200,6 +200,13 @@ object KExpressions {
         return Expressions.concat(left, right)
     }
 
+    fun <PROPERTY> concat(
+        left: PropertyMetamodel<PROPERTY>,
+        right: PropertyMetamodel<PROPERTY>,
+    ): Concat<PROPERTY> {
+        return Expressions.concat(left, right)
+    }
+
     fun <PROPERTY> lower(
         propertyMetamodel: PropertyMetamodel<PROPERTY>,
     ): StringExpression.Lower<PROPERTY> {

doma-kotlin/src/test/kotlin/org/seasar/doma/jdbc/criteria/KNativeSqlSelectTest.kt

@@ -1533,9 +1533,13 @@ internal class KNativeSqlSelectTest {
     @Test
     fun expression_concat() {
         val e = Emp_()
-        val stmt = nativeSql.from(e).select(concat(e.name, "a"))
+        val stmt = nativeSql.from(e).select(
+            concat(e.name, "a"),
+            concat("a", e.name),
+            concat(e.name, e.name),
+        )
         val sql = stmt.asSql()
-        assertEquals("select concat(t0_.NAME, 'a') from EMP t0_", sql.formattedSql)
+        assertEquals("select concat(t0_.NAME, 'a'), concat('a', t0_.NAME), concat(t0_.NAME, t0_.NAME) from EMP t0_", sql.formattedSql)
     }
 
     @Test