RFR: JDK-8248863: Add search landing page to API documentation [v4]

[Hannes Wallnöfer]

> This is the second of two PRs to enhance JavaDoc search, it is based on the first one (#8185).
> 
> It adds a standalone search page (search.html) along with its own script file (search-page.js). This PR is very similar to the last prototype I uploaded and demoed, the changes are mostly tweaks to the markup, style sheets and text. 
> 
> JDK API docs rendered with this patch can be viewed and tested here (top-level files only, updated on April 20th):
> http://cr.openjdk.java.net/~hannesw/8248863/api.02/
> http://cr.openjdk.java.net/~hannesw/8248863/api.02/search.html

Hannes Wallnöfer has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:

 - Merge master
 - Use different max results values for popup and page search
 - Fix search link height
 - First round of feedback
 - JDK-8248863: Add search landing page to API documentation
 - Update copyright headers
 - JDK-8282559: Allow multiple search terms in javadoc search

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Changes: https://git.openjdk.java.net/jdk/pull/8226/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8226&range=03
  Stats: 742 lines in 20 files changed: 678 ins; 7 del; 57 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8226.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8226/head:pull/8226

PR: https://git.openjdk.java.net/jdk/pull/8226