RFR: 8292955: Collections.checkedMap Map.merge does not properly check key and value [v3]

[Per Minborg]

On Thu, 7 Mar 2024 05:33:16 GMT, Lei Zhu <duke at openjdk.org> wrote:

>> When the specified key did not associated with a value, should check the `key` and `value` type.
>
> Lei Zhu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use testNG builtin functionalities and modify the test function name

Adding the checks before remapping seems the right thing to do in order to uphold the checked maps guarantees on types and values.

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Marked as reviewed by pminborg (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18141#pullrequestreview-2081881249