RFR: 8344301: Refine stylesheet for API docs

[Hannes Wallnöfer]

This is an extensive update to the JavaDoc stylesheet that focuses on layout and typography, with the purpose of making API docs easier to read and use.

List of changes:

 - Slightly increase text and navigation fonts to improve readability and to better match the code font (which remains unchanged). 
 - Fix font size and line height inconsistencies in many places.
 - Limit the maximal width of page content to improve readability on large displays. If more horizontal space is available, page content is centered.
 - Remove light gray section background in class and module pages to simplify and unclutter the layout. 
 - Add a subtle gray background to code elements in normal text to set them apart.
 - Highlight headings of member details when they are used as link targets.
 - Reserve use of bold font in member summary tables to element names to make them easier to spot and reduce visual noise.
 - Slightly reduce width of TOC sidebar and use ellipsis (...) if content does not fit (but long signatures continue to wrap).
 - Make method signatures in details easier to read on small dispays by allowing them to wrap before parameters and throws sections.
 - Make tabs on top of summary tables scroll instead of wrapping if they overflow the available horizontal space.
 - Hide TOC sidebar and copy-to-clipboard buttons in addition to the top navigation bar when printing a page.
 - Improve styling of additional HTML doc-files.
 - Remove animations and smooth scrolling in order to improve accessibility.
 - Various cleanup.

There are too many non-trivial changes in the stylesheet to try explaining them here, but of course I'll be happy to discuss every change on request.

[Full JDK API docs are available for testing and comparison](https://cr.openjdk.org/~hannesw/8344301/api.05/index.html).

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Commit messages:
 - Update copyright headers
 - 8344301: Refine stylesheet for API docs

Changes: https://git.openjdk.org/jdk/pull/23678/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23678&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344301
  Stats: 281 lines in 5 files changed: 114 ins; 88 del; 79 mod
  Patch: https://git.openjdk.org/jdk/pull/23678.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23678/head:pull/23678

PR: https://git.openjdk.org/jdk/pull/23678