RFR: JDK-8277520: Implement JDK-8 default methods for IdentityHashMap [v4]

[ExE Boss]

On Sat, 19 Mar 2022 19:46:19 GMT, ExE Boss <duke at openjdk.java.net> wrote:

>> liach has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - merge branch 'identityhashmap-bench' of https://github.com/liachmodded/jdk into identityhashmap-default
>>  - fix whitespace
>
> src/java.base/share/classes/java/util/IdentityHashMap.java line 523:
> 
>> 521:      *          mapping was in the map
>> 522:      */
>> 523:     private boolean removeMapping(Object key, Object value) {
> 
> Note that `IdentityHashMap.remove(Object, Object)` needs to call this method, as the default implementation calls `Objects.equals(…)`: <https://github.com/openjdk/jdk/blob/3f923b82c31325504430b50dee262fd460004e7b/src/java.base/share/classes/java/util/Map.java#L866-L874>

This is being addressed in <https://github.com/openjdk/jdk/pull/8259>.

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PR: https://git.openjdk.java.net/jdk/pull/6532