RFR: 8305746: InitializeEncoding should cache Charset object instead of charset name [v3]

[Peter Hofer]

> Store `Charset` object in `jnuEncoding` and use `String(byte[], Charset)` and `String.getBytes(Charset)` instead of passing the charset name.

Peter Hofer has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into JDK-8305746
 - Rename jnuEncoding to jnuCharset.
 - 8305746: InitializeEncoding should cache Charset object instead of charset name

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13499/files
  - new: https://git.openjdk.org/jdk/pull/13499/files/9f2494d5..9d10b1da

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13499&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13499&range=01-02

  Stats: 445 lines in 39 files changed: 226 ins; 81 del; 138 mod
  Patch: https://git.openjdk.org/jdk/pull/13499.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13499/head:pull/13499

PR: https://git.openjdk.org/jdk/pull/13499