RFR: 8268764: Use Long.hashCode() instead of int-cast where applicable

[Сергей Цыпанов]

In some JDK classes there's still the following hashCode() implementation:

long objNum;

public int hashCode() {
    return (int) objNum;
}

This outdated expression should be replaced with Long.hashCode(long) as it

- uses all bits of the original value, does not discard any information upfront. For example, depending on how you are generating the IDs, the upper bits could change more frequently (or the opposite).

- does not introduce any bias towards values with more ones (zeros), as it would be the case if the two halves were combined with an OR (AND) operation.

See https://stackoverflow.com/a/4045083

This is related to https://github.com/openjdk/jdk/pull/4309

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Commit messages:
 - 8268764: Use Long.hashCode() instead of int-cast where applicable

Changes: https://git.openjdk.java.net/jdk/pull/4491/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4491&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268764
  Stats: 15 lines in 9 files changed: 6 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4491.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4491/head:pull/4491

PR: https://git.openjdk.java.net/jdk/pull/4491