[jdk19] RFR: 8067757: Incorrect HTML generation for copied javadoc with multiple @throws tags

[Pavel Rappo]

Please review this PR for JDK 19.

This PR fixes JDK-8067757. To understand what JDK-8067757 is about, you first need to understand how javadoc documents the fact that such and such exceptions are thrown by a constructor or method.

If a constructor or method declaration indicates thrown exceptions, javadoc creates the "Throws:" section in that declaration documentation. Here's the algorithm which javadoc uses to fill in that section:

1. For each `@throws` tag that is directly present on the declaration, add an entry to the section.
2. If this is a method declaration, then for those exceptions from that declaration's `throws` clause for which there were no `@throws` tags found in step 1, try to inherit `@throws` tags from the overridden methods found as per Method Comments Algorithm[^1].
3. For each of the remaining exceptions from the `throws` clause (i.e. the exceptions for which documentation could neither be found in step 1, nor inherited in step 2), add an entry that mentions the exception but has no description. 

The problem that JDK-8067757 is concerned with is that if an exception is documented using multiple `@throws` tags, only one of these tags will be inherited in step 2.

While fixing this issue I discovered an unpleasant interference with JDK-4947455[^2] and fixed it.

Looking ahead, JDK-6509045[^3] is about a similar problem that happens in step 1 in the presence of `{@inheritDoc}`. I'm also planning to fix JDK-6509045 in JDK 19.

[^1]: https://docs.oracle.com/en/java/javase/18/docs/specs/javadoc/doc-comment-spec.html#method-comments-algorithm
[^2]: https://bugs.openjdk.org/browse/JDK-4947455
[^3]: https://bugs.openjdk.org/browse/JDK-6509045

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Commit messages:
 - refactor: move TagletWriter to the end of params
 - refactor: make the throwsTagsOutput method private
 - refactor: use var for Utils and CommentHelper
 - fix: clarify the throwsTagsOutput doc comment
 - fix: remove interference with subexceptions
 - related: simplify skipping condition
 - related: refactor CommentHelper.getExceptionName
 - fix: improve the doc comment
 - fix: update the "already documented" set later
 - related: remove a nearby typo

Changes: https://git.openjdk.org/jdk19/pull/95/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk19&pr=95&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8067757
  Stats: 418 lines in 5 files changed: 361 ins; 13 del; 44 mod
  Patch: https://git.openjdk.org/jdk19/pull/95.diff
  Fetch: git fetch https://git.openjdk.org/jdk19 pull/95/head:pull/95

PR: https://git.openjdk.org/jdk19/pull/95