RFR: 8345292: Improve javadocs for MemorySegment::getStrings defining word boundary cases [v5]

[Per Minborg]

> This PR proposes to improve the 'MemorySegment.getString(long offset, Charset charset)` method documentation with respect to multi-octet concerns.

Per Minborg has updated the pull request incrementally with two additional commits since the last revision:

 - Remove imp note
 - Add text on N octets

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25715/files
  - new: https://git.openjdk.org/jdk/pull/25715/files/4ea36452..5f5b1473

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25715&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25715&range=03-04

  Stats: 12 lines in 1 file changed: 8 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25715.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25715/head:pull/25715

PR: https://git.openjdk.org/jdk/pull/25715