RFR: JDK-8263261 Extend String::translateEscapes to support unicode escapes

[Jim Laskey]

Currently String::translateEscapes does not support unicode escapes, reported as a IllegalArgumentException("Invalid escape sequence: ..."). String::translateEscapes should translate unicode escape sequences to provide full coverage,

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Commit messages:
 - Unicode escape sequences in translateEscapes

Changes: https://git.openjdk.org/jdk/pull/17491/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17491&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8263261
  Stats: 56 lines in 2 files changed: 50 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17491.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17491/head:pull/17491

PR: https://git.openjdk.org/jdk/pull/17491