RFR: JDK-8254052: improve type specificity of TagletWriter and friends [v5]

[Hannes Wallnöfer]

On Fri, 16 Oct 2020 23:19:19 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

>> The types of `DocTree` parameters in some methods in `TagletWriter` can be changed from `DocTree` to more specific subtypes. Doing so makes the code less prone to incorrect calls, and removes the need for downcasting the argument in the method bodies.
>> 
>> This means the implementation of those methods can often be simplified.
>> 
>> In addition, the call sites need to be improved, and with the help of some improvements to methods in `Utils`, the methods that access different kinds of trees can return the lists using a more specific subtype as well.
>> 
>> Finally, a quick analysis of some of the `Utils` methods to access different kinds of trees shows that there are some more convenient methods that can be used instead.
>
> Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:
> 
>   post-merge fix

Looks good, sorry for missing the incremental review.

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Marked as reviewed by hannesw (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/517