RFR: JDK-8164094: javadoc allows to create a @link to a non-existent method

[Hannes Wallnöfer]

Please review a simple fix in `JavacTrees` to only look up member references in the enclosing type if the reference does not contain an explicit type name. For example, `@see #method()` in a a doc comment of class `Outer.Inner` should find method `Outer.method()`, but `@see Inner#method()` should not (regardless of comment location).

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Commit messages:
 - Additional test
 - JDK-8164094: javadoc allows to create a @link to a non-existent method

Changes: https://git.openjdk.org/jdk/pull/17069/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17069&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8164094
  Stats: 56 lines in 2 files changed: 29 ins; 1 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/17069.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17069/head:pull/17069

PR: https://git.openjdk.org/jdk/pull/17069