RFR: JDK-8280402: Add new convenience forms to HtmlTree [v2]

[Jonathan Gibbons]

> Please review a simple `noreg-clean` update to `HtmlTree` and a couple of friends.  The updates are to continue the trend towards the use of Facebook tory methods for `HtmlTree` objects, and to leverage generic methods and lambdas to generate composite content. The cleanup is mostly extracted from some parallel work for a separate PR.  Some of the more general cleanup was suggested by an IDE.
> 
> All javadoc tests pass locally; I have a job in  progress to validate the fix on all platforms, although there is no reason to believe there might be any issues.

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

  fix whitespace

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7166/files
  - new: https://git.openjdk.java.net/jdk/pull/7166/files/58a63f32..75a69eae

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7166&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7166&range=00-01

  Stats: 9 lines in 2 files changed: 3 ins; 1 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7166.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7166/head:pull/7166

PR: https://git.openjdk.java.net/jdk/pull/7166