RFR: JDK-8258659: Eliminate whitespace comments from generated pages

Fri Dec 18 04:25:01 UTC 2020

Empty comments were being used to stop empty nodes being optimized away in `HtmlTree.add`, but the empty comments caused annoying noise in the generated docs.  A better solution is to use `HtmlTree.EMPTY`, which had the right effect, without the unwanted side-effects.

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

Commit messages:
 - JDK-8258659: Eliminate whitespace comments from generated pages

Changes: https://git.openjdk.java.net/jdk/pull/1836/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1836&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258659
  Stats: 27 lines in 4 files changed: 0 ins; 17 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1836.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1836/head:pull/1836

PR: https://git.openjdk.java.net/jdk/pull/1836