RFR: JDK-8277420: Provide a way to copy the hyperlink to a doc element to the clipboard [v3]

[Hannes Wallnöfer]

> This is a CSS/JavaScript only change to implement copy-to-clipboard functionality for all headers (`h1` - `h6`) that have an `id` attribute associated with them. The following element-attribute patterns are supported (using `<h2>` as an example):
> 
>  - `<section id="..."><h2>` (generated by javadoc)
>  - `<h2 id="...">` (commonly used)
>  - `<h2><a id="...">` (legacy)
> 
> The change includes a consolidation of the CSS styles used to render copy-to-clipboard buttons, of which we have now three kinds: for snippets, for the link on the search page, and for headers. There is now a base CSS class called "copy" that defines the styles shared by all copy-to-clipboard buttons, and additional CSS properties for the concrete "subclasses". 
> 
> API docs generated with this change can be viewed here (top level files and java.base module):
> http://cr.openjdk.java.net/~hannesw/8277420/api.03/

Hannes Wallnöfer has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Update new snippet test for CSS changes
 - Merge branch 'master' into JDK-8277420
 - Fix jquery selector for anchor within header
 - Clean up copy-to-clipboard button styles
 - JDK-8277420: Provide a way to copy the hyperlink to a doc element to the clipboard

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8817/files
  - new: https://git.openjdk.java.net/jdk/pull/8817/files/b84eb5d2..541f124d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8817&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8817&range=01-02

  Stats: 40392 lines in 791 files changed: 9876 ins; 27972 del; 2544 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8817.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8817/head:pull/8817

PR: https://git.openjdk.java.net/jdk/pull/8817