FSIndexComparatorImpl.equalsWithoutType() gets slow for many CASes with the same TS

When creating several hundred CASes with the same type system, the `shareExisting` mechanism which is designed to save on memory starts eating into CPU time quite a lot.

This screenshot shows that in my particular case, the method is called ~11mio times and takes the bulk of the processing time. The call hierarchy is a bit messed up though - actually this happens when the CASes are initialized.

The second screenshot shows the actual call hierarchy, but for some reason, the profile doesn't properly dive into the `equals` method here and doesn't count the time spent in `equalsWithoutType`.

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So either the method shouldn't be called that often - or - it should be way faster.

In the example, I have like 1800 CAS instances and their type system has upwards of 200 types.