RFR: 8261254: Initialize charset mapping data lazily

[Claes Redestad]

This patch refactor JDK internal charsets to initialize charset mapping data lazily when needed via holder classes. This means both a startup improvement in some cases, and possible throughput improvements for all DoubleByte-based Charsets.

Testing: tier1-3

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Commit messages:
 - Merge branch 'master' into lazy_charsets
 - More finals, copyrights
 - Improve finality
 - Initialize charset mapping data lazily

Changes: https://git.openjdk.java.net/jdk/pull/2449/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2449&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261254
  Stats: 274 lines in 21 files changed: 24 ins; 59 del; 191 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2449.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2449/head:pull/2449

PR: https://git.openjdk.java.net/jdk/pull/2449