RFR: 8284637: Improve String.join performance [v2]

[XenoAmess]

> 8284637: Improve String.join performance

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

  add jmh

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8169/files
  - new: https://git.openjdk.java.net/jdk/pull/8169/files/e6cf3fa2..9df28a89

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8169&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8169&range=00-01

  Stats: 65 lines in 1 file changed: 65 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8169.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8169/head:pull/8169

PR: https://git.openjdk.java.net/jdk/pull/8169