jmx-dev RFR: 8285149: Using HashMap.newHashMap to replace new HashMap(int)

[XenoAmess]

These are the changes that too many to be reviewed in 8186958, thus split some of them out.

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Commit messages:
 - 9073085: ues HashMap.newHashMap to replace new HashMap(int)

Changes: https://git.openjdk.java.net/jdk/pull/8301/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8301&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285149
  Stats: 36 lines in 20 files changed: 0 ins; 0 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8301.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8301/head:pull/8301

PR: https://git.openjdk.java.net/jdk/pull/8301