RFR: 8372055: Fragment link tag does not work in package info [v2]

[Hannes Wallnöfer]

> Please review a change to make unqualified anchor references such as `{@link ##anchor link}` work everywhere. Previously, such links only worked in class pages. The fix consists in attributing the correct Element in `JavacTrees::attributeDocReference` for references declared in API elements, and setting it to `null` for references defined in `doc-files` to make them work as local links.
> 
> Because of unattributed `doc-files` references, we also have to exclude such links from the reference check in DocLint. This is fine because local references always have a target element, and we do not check the anchor anyway.

Hannes Wallnöfer has updated the pull request incrementally with one additional commit since the last revision:

  Review feedback

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28372/files
  - new: https://git.openjdk.org/jdk/pull/28372/files/a9f5d0a2..8cf42e3e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28372&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28372&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28372.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28372/head:pull/28372

PR: https://git.openjdk.org/jdk/pull/28372