RFR: 8358015: Fix SequencedMap sequenced view method specifications [v3]

[Jaikiran Pai]

On Wed, 4 Jun 2025 06:24:57 GMT, Stuart Marks <smarks at openjdk.org> wrote:

>> For a full explanation, see the bug report [JDK-8358015](https://bugs.openjdk.org/browse/JDK-8358015).
>> 
>> This PR includes three related changes:
>> * New overrides in SequencedMap view collection implementations, which improve their behavior.
>> * Update to `@implSpec` clauses to reflect this behavior (which was previously ill-specified).
>> * Update to a test which relied on unspecified behavior.
>
> Stuart Marks has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8358015-SequencedMap-view-implSpecs
>  - Tweak nsee() declaration; adjust specs per suggestion; update copyrights.
>  - Update @implSpecs of SequencedMap view methods.
>  - Update SequencedMap views to use SequencedMap methods instead of inheriting
>    default methods from SequencedCollection.

Marked as reviewed by jpai (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/25515#pullrequestreview-2895381564