RFR: 8309881: Qualified name of a type element depends on its origin (source vs class)

[Adam Sotona]

`javax.lang.model.type.TypeMirror::toString` says: "Any names embedded in the result are qualified if possible."
However in reality the form of the names depends on the source vs.class origin.

This patch enforces qualified name to be used.

Please review.

Thanks,
Adam

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Commit messages:
 - 8309881: Qualified name of a type element depends on its origin (source vs class)

Changes: https://git.openjdk.org/jdk/pull/18917/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18917&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309881
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18917.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18917/head:pull/18917

PR: https://git.openjdk.org/jdk/pull/18917