RFR: 8306374: (bf) Improve performance of DirectCharBuffer::append(CharSequence[,int,int]) [v6]

[Brian Burkhalter]

> Use `getChars()` to copy characters to an intermediate local `char[]` array and then `putArray()` to copy the chars into the buffer itself.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8306374: Do not generate appandChars() for read-only cases

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13522/files
  - new: https://git.openjdk.org/jdk/pull/13522/files/739c33ab..801f3619

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13522&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13522&range=04-05

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13522.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13522/head:pull/13522

PR: https://git.openjdk.org/jdk/pull/13522