RFR: 8305746: InitializeEncoding should cache Charset object instead of charset name [v2]

[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 pull request now contains one commit:

  8305746: InitializeEncoding should cache Charset object instead of charset name

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Changes: https://git.openjdk.org/jdk/pull/13499/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13499&range=01
  Stats: 49 lines in 1 file changed: 18 ins; 14 del; 17 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