RFR: 8305811: (bf) Improve performance of CharBuffer::append(CharSequence[,int,int]) [v9]

[Brian Burkhalter]

> Use the `getChars` method of `String`, `StringBuffer`, and `StringBuilder` to load the chars directly into the array of the heap buffer.

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

  8305811: Add comments about special casing in append(CharSequence)

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13415/files
  - new: https://git.openjdk.org/jdk/pull/13415/files/ab5fe71c..c18565eb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13415&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13415&range=07-08

  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13415.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13415/head:pull/13415

PR: https://git.openjdk.org/jdk/pull/13415