RFR: JDK-8253559: The INDEX page should link to Serialized Form and Constant Values pages [v4]

[Jonathan Gibbons]

> The mechanism to add links for summary pages in the main index is generalized, and now includes the Constant Values
> page, the Deprecated page and the Serialized Form page, provided these pages have non-empty content.
> The only change to the generated output is very minor: the text of existing link to the "System Properties" page is
> changed to use a non-breaking space, in line with the links for "All Classes" and "All Packages".

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

  revert changes related to "All Classes" and "All Packages" per review feedback

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/643/files
  - new: https://git.openjdk.java.net/jdk/pull/643/files/c37c7367..c4de6a15

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=643&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=643&range=02-03

  Stats: 23 lines in 5 files changed: 13 ins; 0 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/643.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/643/head:pull/643

PR: https://git.openjdk.java.net/jdk/pull/643