RFR: 8361715: (bf) Improve java/nio/Buffer/GetChars.java and migrate to JUnit [v3]

[Brett Okken]

> junit for CharSequence behavior of CharBuffer covering different CharBuffer implementations in various states (offset, position, limit)

Brett Okken has updated the pull request incrementally with one additional commit since the last revision:

  add coverage for ByteBuffer as CharBuffer and test for codePoints

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26282/files
  - new: https://git.openjdk.org/jdk/pull/26282/files/b74bb50c..bc3f5771

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26282&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26282&range=01-02

  Stats: 58 lines in 1 file changed: 58 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26282.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26282/head:pull/26282

PR: https://git.openjdk.org/jdk/pull/26282