RFR: JDK-8253559: The INDEX page should link to Serialized Form and Constant Values pages [v3]

[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 two additional commits since the last revision:

 - fix whitespace typo
 - move all summary pages to "Tags" category

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/643/files
  - new: https://git.openjdk.java.net/jdk/pull/643/files/58121383..c37c7367

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=643&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=643&range=01-02

  Stats: 43 lines in 11 files changed: 11 ins; 17 del; 15 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