[#4380] Make dialect-specific DSL constructors protected to allow further subtyping

jOOQ/src/main/java/org/jooq/util/cubrid/CUBRIDDSL.java

@@ -54,7 +54,7 @@ public class CUBRIDDSL extends DSL {
     /**
      * No instances
      */
-    private CUBRIDDSL() {
+    protected CUBRIDDSL() {
     }
 
     // -------------------------------------------------------------------------

jOOQ/src/main/java/org/jooq/util/derby/DerbyDSL.java

@@ -53,6 +53,6 @@ public class DerbyDSL extends DSL {
     /**
      * No instances
      */
-    private DerbyDSL() {
+    protected DerbyDSL() {
     }
 }

jOOQ/src/main/java/org/jooq/util/firebird/FirebirdDSL.java

@@ -53,6 +53,6 @@ public class FirebirdDSL extends DSL {
     /**
      * No instances
      */
-    private FirebirdDSL() {
+    protected FirebirdDSL() {
     }
 }

jOOQ/src/main/java/org/jooq/util/h2/H2DSL.java

@@ -53,6 +53,6 @@ public class H2DSL extends DSL {
     /**
      * No instances
      */
-    private H2DSL() {
+    protected H2DSL() {
     }
 }

jOOQ/src/main/java/org/jooq/util/hsqldb/HSQLDBDSL.java

@@ -53,6 +53,6 @@ public class HSQLDBDSL extends DSL {
     /**
      * No instances
      */
-    private HSQLDBDSL() {
+    protected HSQLDBDSL() {
     }
 }

jOOQ/src/main/java/org/jooq/util/mariadb/MariaDBDSL.java

@@ -55,7 +55,7 @@ public class MariaDBDSL extends DSL {
     /**
      * No instances
      */
-    private MariaDBDSL() {
+    protected MariaDBDSL() {
     }
 
     // -------------------------------------------------------------------------

jOOQ/src/main/java/org/jooq/util/mysql/MySQLDSL.java

@@ -55,7 +55,7 @@ public class MySQLDSL extends DSL {
     /**
      * No instances
      */
-    private MySQLDSL() {
+    protected MySQLDSL() {
     }
 
     // -------------------------------------------------------------------------

jOOQ/src/main/java/org/jooq/util/postgres/PostgresDSL.java

@@ -63,7 +63,7 @@ public class PostgresDSL extends DSL {
     /**
      * No instances
      */
-    private PostgresDSL() {}
+    protected PostgresDSL() {}
 
     // -------------------------------------------------------------------------
     // PostgreSQL-specific array functions

jOOQ/src/main/java/org/jooq/util/sqlite/SQLiteDSL.java

@@ -54,7 +54,7 @@ public class SQLiteDSL extends DSL {
     /**
      * No instances
      */
-    private SQLiteDSL() {
+    protected SQLiteDSL() {
     }
 
     // -------------------------------------------------------------------------