RFR: JDK-8263528: Make static page ids safe from collision with language elements

[Hannes Wallnöfer]

A simple change to make the HTML ids used for search input and reset button safe from collision with Java elements. The ids are also added th the `HtmlIds` class instead of using strings.

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Commit messages:
 - JDK-8263528: Make static page ids safe from collision with language elements

Changes: https://git.openjdk.java.net/jdk/pull/2973/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2973&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263528
  Stats: 21 lines in 7 files changed: 2 ins; 0 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2973.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2973/head:pull/2973

PR: https://git.openjdk.java.net/jdk/pull/2973