[jdk17u] RFR: 8274242: Implement fast-path for ASCII-compatible CharsetEncoders on x86

[Claes Redestad]

Clean backport of JDK-8274242

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Commit messages:
 - Backport aaa36cc0069043e34b47e89769eb9eba39e5362a

Changes: https://git.openjdk.java.net/jdk17u/pull/310/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=310&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274242
  Stats: 783 lines in 28 files changed: 392 ins; 355 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/310.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/310/head:pull/310

PR: https://git.openjdk.java.net/jdk17u/pull/310