RFR: 8323746: Add PathElement hashCode and equals [v2]

[Maurizio Cimadamore]

On Fri, 2 Feb 2024 07:41:16 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR proposes to implement `hashCode()` and `equals()` methods for implementations of `PathElement`.
>> 
>> In doing so, the previous `PathElementImpl` was removed and replaced in favor of distinct `record` implementations, each reflecting its own path element selection type. This also allowed the `PathKind` to be removed as this piece of information is now carried in the sealed type hierarchy. 
>> 
>> It is worth noting, the implementations resides in the `jdk.internal` package and consequently, they are not exposed to clients. So, we could use pattern matching (for example) internally but not in client code.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Make all PathElements records

Marked as reviewed by mcimadamore (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17651#pullrequestreview-1860956786