RFR: 8253733: taglet api

[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 taglets and which are used for block taglets.

Some dead code is removed, and the doc comments are generally cleaned up as well.  More details are given in the JBS
issue.

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Commit messages:
 - Update AbstractMemberWriter
 - Cleanup Taglet API

Changes: https://git.openjdk.java.net/jdk/pull/406/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=406&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253733
  Stats: 396 lines in 28 files changed: 96 ins; 97 del; 203 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