[jdk17u] Integrated: 8275863: Use encodeASCII for ASCII-compatible DoubleByte encodings

[Claes Redestad]

Clean backport of JDK-8275863

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

Commit messages:
 - Backport 6c05cc9d15fb6014b8293a66ef132f3461badca1

Changes: https://git.openjdk.java.net/jdk17u/pull/311/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=311&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275863
  Stats: 35 lines in 5 files changed: 24 ins; 4 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/311.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/311/head:pull/311

PR: https://git.openjdk.java.net/jdk17u/pull/311