RFR: 8302284: Webview loaded webpage is not showing play, volume related buttons for embeded Audio/Video elements

[Jay Bhaskar]

Issue: default html5 video element not showing media controls
Details: Media control design has been refactored in the current Webkit Gtk port. The CSS id 
                and properties related to media buttons, and slider have been removed, due to which the 
                media style mediaControlsAdwaita.css values are not being applied.
Solution: restored media control keywords and mapped to CSS keywords values.

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Commit messages:
 - 8302284: Webview loaded webpage is not showing play, volume related buttons for embeded Audio/Video elements

Changes: https://git.openjdk.org/jfx/pull/1049/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1049&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302284
  Stats: 79 lines in 4 files changed: 79 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1049.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1049/head:pull/1049

PR: https://git.openjdk.org/jfx/pull/1049