CSV DataSet thread and thread group sharing might not work due to identityHashCode

@vlsi ([Bug 57910](https://bz.apache.org/bugzilla//show_bug.cgi?id=57910&redirect=false)):
CSVDataSet uses identityHashCode to make "unique" id for thread group and thread: https://github.com/apache/jmeter/blob/aa210850885837e7f9f58c49e0a5f503a7eb4cca/src/components/org/apache/jmeter/config/CSVDataSet.java#L166-170

In fact it does not always work, since identityHashCodes could return duplicate values for different objects.

Even codes for thread group and thread could be the same.

Something more unique should be used to implement "share mode".

Severity: normal
OS: All

Start with src/components/org/apache/jmeter/config/CSVDataSet.java at lines 166-170 and inspect how identityHashCode values form the thread-group and thread sharing identifiers. Determine how collisions can occur, including between a thread group and a thread, then define a replacement that keeps share-mode identifiers distinct. Done means the sharing mechanism no longer depends on potentially duplicate identityHashCode values.

Written by the indexing model from the issue text.