RFR: 8333843: Provide guidelines on MemorySegment to read strings with known lengths [v3]

[Per Minborg]

> This PR proposes to add a new overload to `MemorySegment::getString` whereby it is possible to pass in a known byte length of the content in a segment that should be converted to a String. This is useful in case one already knows the byte length and thereby does not need to scan for a null terminator.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Update after comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20725/files
  - new: https://git.openjdk.org/jdk/pull/20725/files/cc862a05..976d4465

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20725&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20725&range=01-02

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20725.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20725/head:pull/20725

PR: https://git.openjdk.org/jdk/pull/20725