Feature: Fullscreen Video Playback with Interactive Controls

[Dawnflare]

Description

This PR introduces a highly requested Fullscreen Video Playback feature to the Extra Metadata Loader.

Currently, the WPF MediaElement is constrained by the parent grid (such as the Harmony theme's game details panel). This enhancement allows users to seamlessly pop the video out into a borderless, topmost, maximized window for a proper viewing experience.

Implementation Details

• Added a new Fullscreen toggle button to the existing EML video control bar.
• Implemented a MouseDoubleClick event on the video surface as a secondary trigger.
• Built a seamless state-handoff: When triggered, the embedded player pauses, captures the current TimeSpan position, volume, and mute state, and passes them to a dynamically generated maximized WPF Window containing a new MediaElement.
• Closing the fullscreen window (via the Escape key, double-click, or the UI exit button) returns the timestamp, volume, and mute state back to the embedded player and resumes playback seamlessly.
• New Fullscreen Transport Controls: Added an unobtrusive, animated control bar at the bottom of the fullscreen window. Features include:
  • Play/Pause toggle (also mapped to Spacebar and single-click).
  • Seekable timeline slider with live position updates.
  • Volume control slider and a dedicated mute button (also mapped to the 'M' key).
  • Premium Aesthetics: The control bar and exit button rest at a subtle 15% opacity and seamlessly fade in to 90% opacity over 200ms when hovered.
• Bug Fixes: Included robust WPF workarounds to ensure initial frames properly render when opening the player in a paused state, preventing black screens or unintended stream resets.

Testing

Compiled and tested successfully locally against standard 1080p H.264 MP4 files. The audio sink states cleanly translate back to the embedded view without getting de-synced.