RFR: 8325340: Add ASCII fast-path to Data-/ObjectInputStream.readUTF

[Claes Redestad]

Adding a fast-path for ASCII-only modified UTF-8 strings deserialied via Data- and ObjectInputStream

Testing: tier1-3

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Commit messages:
 - Merge branch 'master' into io_utf8_fastpath
 - Reduce cost for small Strings in DataInputStream
 - Optimize away StringBuilder for strings smaller than CHAR_BUF_SIZE chars, add more micros, minor improvements
 - Sync up DataInputStreamTest to make results comparable with ObjectInputStreamTest, fix a buffer overrun issue in ObjectInputStream
 - Remove stray code
 - Clean up DataInputStream.readUTF/readUTFChars
 - Use ISO-8859-1 to avoid back-to-back countPositives scans
 - Rearrange JLA
 - Add ASCII fast-path to Data-/ObjectInputStream.readUTF

Changes: https://git.openjdk.org/jdk/pull/17734/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17734&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325340
  Stats: 413 lines in 4 files changed: 375 ins; 15 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/17734.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17734/head:pull/17734

PR: https://git.openjdk.org/jdk/pull/17734