[jOOQ/jOOQ#7106] More transaction statement support (WIP)

This includes:
- EXASOL implementation

jOOQ/src/main/java/org/jooq/impl/AbstractQuery.java

@@ -42,6 +42,7 @@ import static java.lang.Boolean.TRUE;
 import static org.jooq.Constants.FULL_VERSION;
 import static org.jooq.ExecuteType.DDL;
 // ...
+// ...
 import static org.jooq.SQLDialect.FIREBIRD;
 import static org.jooq.SQLDialect.HSQLDB;
 // ...

jOOQ/src/main/java/org/jooq/impl/StartTransaction.java

@@ -95,6 +95,13 @@ implements
 
 
 
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             case FIREBIRD: {
                 // [#7106] Blocks can't start new transactions
                 if (ctx.data(DATA_BLOCK_NESTING) == null)