[FLINK-35762] Cache hashCode for TableID & Transform descriptors

[yuxiqian]

This closes FLINK-35762.

As previously discussed offline with @lvyanquan, HashMap lookup could be slow since we must calculate key hash code every time, though most key objects are immutable.

A common practice in Java world is caching object hash code in a transient field, just like what java.lang.String does. In CDC code, TableId & transform rule types are frequently used as HashMap key type, and their hash code could be safely cached since their instances are immutable.

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