RFR: JDK-8253733: Cleanup internal taglet API [v3]

[Jonathan Gibbons]

> This is a general cleanup of various classes related to the handling of tags and taglets in the standard doclet.
> 
> The initial motivation was to clean up static methods on `TagletWriter` that took a `TagletWriter` as a parameter.
> These methods are converted into instance methods, and the call sites simplified as well.
> Another area of cleanup is to make clear which methods are used for inline tags and which are used for block tags.
> 
> Some dead code is removed, and the doc comments are generally cleaned up as well.  More details are given in the JBS
> issue.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  Add an ILA check for getBlockTagOutput

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/406/files
  - new: https://git.openjdk.java.net/jdk/pull/406/files/a55db493..8cd2fd0a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=406&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=406&range=01-02

  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/406.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/406/head:pull/406

PR: https://git.openjdk.java.net/jdk/pull/406