RFR: 8364320: String encodeUTF8 latin1 with negatives

[Brett Okken]

As suggested on mailing list, when encoding latin1 bytes to utf-8, we can count the leading positive bytes and in the case where there is a negative, we can copy all the positive values to the target byte[] prior to processing the remaining data 1 byte at a time.

https://mail.openjdk.org/pipermail/core-libs-dev/2025-July/149417.html

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Commit messages:
 - whitespace
 - use counted positive values when converting latin1 to utf-8

Changes: https://git.openjdk.org/jdk/pull/26597/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26597&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364320
  Stats: 9 lines in 1 file changed: 6 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26597.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26597/head:pull/26597

PR: https://git.openjdk.org/jdk/pull/26597