RFR: 8338611: java.lang.module specification wording not aligned with JEP 261

[Mark Reinhold]

The `java.lang.module` package specification defines the default set of root modules as “every module that is observable on the upgrade module path or among the system modules, and that exports at least one package without qualification.” There’s no need to use the term “observable” here, since any module in those two locations is, by definition, observable.

This should be changed to align with the wording in [JEP 261](https://openjdk.org/jeps/261#root-modules): “every module on the upgrade module path or among the system modules that exports at least one package, without qualification.”

This is not a substantive specification change, so a CSR is not required.

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Commit messages:
 - 8338611: java.lang.module specification wording not aligned with JEP 261

Changes: https://git.openjdk.org/jdk/pull/20632/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20632&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338611
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20632.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20632/head:pull/20632

PR: https://git.openjdk.org/jdk/pull/20632