[JDBC] StatementImpl

[chernser]

Description

There are some issues that should be addressed in StatementImpl:

• add more test for uncovered methods
• test close() in concurrent case and check all child resources are properly closed. Same for cancel()
• enquoteLiteral(String val) needs review

Implement next methods:

• isClosed()
• setLargeMaxRows(long max)
• getLargeMaxRows()
• enquoteIdentifier
• isSimpleIdentifier(String identifier)
• enquoteNCharLiteral(String val)
• closeOnCompletion()