RFR: 8325152: Clarify specification of java.io.RandomAccessFile.setLength

[Brian Burkhalter]

Modify the specification verbiage of `java.io.RandomAccessFile.setLength` to account for the effect of the method on the file offset as returned by `getFilePointer`.

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Commit messages:
 - 8325152: Clarify specification of java.io.RandomAccessFile.setLength

Changes: https://git.openjdk.org/jdk/pull/17679/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17679&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325152
  Stats: 20 lines in 1 file changed: 9 ins; 2 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/17679.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17679/head:pull/17679

PR: https://git.openjdk.org/jdk/pull/17679