Added read-committed transaction isolation and consistency support to TransactionAwareCacheDecorator

[werner77]

The decorator now maintains consistency within the transaction and ensures all changes are only committed to the target cache on successful completion of the transaction.

• Added complete isolation and consistency support for concurrent transactions.
• Added accompanying Javadoc documentation.
• Added unit test testing the isolation properties introduced.
• Maintained backwards compatibility (existing unit test is still there and succeeds)

See also issue: https://github.com/spring-projects/spring-framework/issues/17353