RFR: 8294397: Replace StringBuffer with StringBuilder within java.text

[Justin Lu]

Problem: Unnecessary instances of StringBuffer within java.text (internal only)

Fix: StringBuffer Replaced with StringBuilder, and adjusted variable/method names

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Commit messages:
 - Update PatternEntry test case for StringBuilder
 - Copyright update
 - Replace buffer in both, adjust addToBuilder dependencies
 - Adjust variable names within DigitList
 - Fix: Replace StringBuffer in CollationElementIterator
 - Fix: replace StringBuffer with StringBuilder

Changes: https://git.openjdk.org/jdk/pull/10475/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10475&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294397
  Stats: 35 lines in 5 files changed: 0 ins; 0 del; 35 mod
  Patch: https://git.openjdk.org/jdk/pull/10475.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10475/head:pull/10475

PR: https://git.openjdk.org/jdk/pull/10475