RFR: JDK-8325687: SimpleJavaFileObject specification would benefit from implSpec

[Joe Darcy]

While reading the spec in the context of another potential change, noticed some cases where using implSpec would lead to a better structured specification.

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Commit messages:
 - JDK-8325687: SimpleJavaFileObject specification would benefit from implSpec

Changes: https://git.openjdk.org/jdk/pull/17854/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17854&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325687
  Stats: 41 lines in 2 files changed: 8 ins; 9 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/17854.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17854/head:pull/17854

PR: https://git.openjdk.org/jdk/pull/17854