* Add SchemaContexts.getExecutorKernel()

* Use SchemaContexts.getExecutorKernel()

* Remove RuntimeContext.executorKernel

* Remove RuntimeContext.executorKernel

* Add SchemaContexts.getSQLParserEngine

* Use SchemaContexts.getSQLParserEngine

* Remove RuntimeContext.sqlParserEngine

* Remove RuntimeContext

* Refactor MySQLComStmtPrepareExecutor

* Refactor SchemaContexts

* Remove SchemaContext

* Refactor SchemaContextsBuilder