[jdk11u-dev] RFR: 8231717: Improve performance of charset decoding when charset is always compactable

[Dmitry Chuyko]

This change improves charset decoding for a number of encodings that are "Latin1Decodable". Original patch applies cleanly.

Testing: tier1, tier2, sun/nio/cs on aarch64 and x86.

StrCodingBenchmark benchmark shows improvements for target encodings (IBM037 etc.) on both aarch64 and x86.

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Commit messages:
 - [PATCH] Backport 0dbfc97c05218ffd10242901d73c0715ccb53bf3

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/58/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=58&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8231717
  Stats: 66 lines in 5 files changed: 60 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/58.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/58/head:pull/58

PR: https://git.openjdk.java.net/jdk11u-dev/pull/58