RFR: 8272687: Replace StringBuffer with StringBuilder in RuleBasedCollator

[Justin Lu]

Problem: Unnecessary instances of StringBuffer + .toString()

Fix: StringBuffer Replaced with StringBuilder, and .toString() removed when possible

Other: Line 698 in RuleBasedCollator.java also uses a .toString() conversion, but removing that instance requires changing the RuleBasedCollationKey constructor's second parameter type from String to StringBuilder

automated testing run passed cleanly

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Commit messages:
 - Copyright update for fix
 - Merge master into fix branch
 - Fix: replace instances of StringBuffer with StringBuilder, drop String conversion

Changes: https://git.openjdk.org/jdk/pull/10432/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10432&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8272687
  Stats: 10 lines in 2 files changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/10432.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10432/head:pull/10432

PR: https://git.openjdk.org/jdk/pull/10432