RFR: 8361715: (bf) Improve java/nio/Buffer/GetChars.java and migrate to JUnit [v5]

[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:

  remove testng GetChars

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26282/files
  - new: https://git.openjdk.org/jdk/pull/26282/files/08151468..198e46e4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26282&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26282&range=03-04

  Stats: 220 lines in 1 file changed: 0 ins; 220 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