RFR: 8273484: Cleanup unnecessary null comparison before instanceof check in java.naming

[Andrey Turbanov]

Update code checks both non-null and instance of a class in java.naming module classes.
The checks and explicit casts could also be replaced with pattern matching for the instanceof operator.
For example:
    The following code:

        return (obj != null &&
                obj instanceof CompoundName &&
                impl.equals(((CompoundName)obj).impl));


Can be simplified to:
    

        return (obj instanceof CompoundName other) &&
                impl.equals(other.impl);


See similar cleanup in java.base - https://bugs.openjdk.java.net/browse/JDK-8258422

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Commit messages:
 - [PATCH] Cleanup unnecessary null comparison before instanceof check in java.naming

Changes: https://git.openjdk.java.net/jdk/pull/5374/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5374&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273484
  Stats: 41 lines in 12 files changed: 0 ins; 11 del; 30 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5374.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5374/head:pull/5374

PR: https://git.openjdk.java.net/jdk/pull/5374