RFR: 8358015: Fix SequencedMap sequenced view method specifications [v2]

[Brent Christian]

On Sat, 31 May 2025 00:47:16 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 incrementally with one additional commit since the last revision:
> 
>   Tweak nsee() declaration; adjust specs per suggestion; update copyrights.

Marked as reviewed by bchristi (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/25515#pullrequestreview-2890167983