RFR: 8287333: Clean up ParamTaglet and ThrowsTaglet [v6]

[Pavel Rappo]

> A cleanup to facilitate fixing bugs like JDK-6509045: `{@inheritDoc}` only copies one instance of the specified exception.

Pavel Rappo has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 37 commits:

 - Merge branch 'master' into 8287333
 - Address feedback
   
   Replaces String with Integer in position map. In contrast with ThrowsTaglet, using String instead of a more suitable type for Input.tagId is not a lossy transformation. So it can still be considered as cleanup. But generally it should be dealt with in 8285488.
 - Merge branch 'master' into 8287333
   
   It's two days before RDP1, the codebase changes quickly. This merge is to keep up with it.
 - Address feedback
   
   Also removes unneeded import.
 - Merge branch 'master' into 8287333
   
   This resolves a conflict in ParamTaglet.
 - Clean up if-branch
 - Remove upper-bounded wildcard
   
   This change simplifies code without any disadvantages:
   
     * Those `List<? extends XTree>` are read-only
     * An argument of the `List<XTree>` type can still be passed to a `List<? extends XTree>` parameter
 - Simplify inheritThrowsDocumentation
 - Reuse more specific variable
 - Merge branch 'master' into 8287333
 - ... and 27 more: https://git.openjdk.java.net/jdk/compare/1aa87e00...418d07b5

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Changes: https://git.openjdk.java.net/jdk/pull/8886/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8886&range=05
  Stats: 422 lines in 4 files changed: 116 ins; 152 del; 154 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8886.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8886/head:pull/8886

PR: https://git.openjdk.java.net/jdk/pull/8886