This refactor some `sun.nio.cs.ext` charsets, such as ISO-2022-CN-GB, ISO-2022-CN-CNS, ISO-2022-KR and a few others to use static rather than per-instance auxiliary decoders. Doing so reduce overheads of calling `charset.newDecoder()`. This reduce or eliminate regressions on `new String(byte[], String)` operations due the removal of thread-local decoder caching in [JDK-8259842](https://bugs.openjdk.java.net/browse/JDK-8259842)
Most ISO-2022 Charsets define a specialized decoder already. The `ISO2022.Decoder` class was only used by `ISO2022_KR`, so folding it into that implementation and simplifying the code brings a rather significant speed-up, both to decoder creation and on actual decoding. Testing: tier1-3, manual runs of sun.nio.cs tests ------------- Commit messages: - Minor cleanup - Reduce decoder creation overheads for sun.nio.cs.ext Charsets Changes: https://git.openjdk.java.net/jdk/pull/2480/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2480&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8261418 Stats: 761 lines in 15 files changed: 258 ins; 411 del; 92 mod Patch: https://git.openjdk.java.net/jdk/pull/2480.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/2480/head:pull/2480 PR: https://git.openjdk.java.net/jdk/pull/2480
