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

[Korov]

When the specified key did not associated with a value, should check the `key` and `value` type.

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Commit messages:
 - 8292955: Collections.checkedMap Map.merge does not properly check key and value
 - 8292955: Collections.checkedMap Map.merge does not properly check key and value
 - 8292955: Collections.checkedMap Map.merge does not properly check key and value

Changes: https://git.openjdk.org/jdk/pull/18141/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18141&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292955
  Stats: 15 lines in 2 files changed: 12 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18141.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18141/head:pull/18141

PR: https://git.openjdk.org/jdk/pull/18141