fix(response-panel): allow full screen and audio for video previews

[princek-bruno]

Summary

Full screen and sound now work in the video response preview, and the player is shaped like the one in the desktop app.

Problem

Jira: VSCODE-63

Playing an mp4 response in the response pane, the picture plays but the full screen and unmute buttons stay greyed out, so the response cannot be viewed large or heard.

Root cause

Webviews run inside a frame that is not permitted to go full screen, so the browser refuses the request and disables its own button. And the editor ships a media build with no decoder for the audio format nearly every mp4 uses, so the player sees no audio track and disables the mute button.

Solution

• Full screen is replaced with an manually added expand toggle that fills the webview, Esc to exit, since the full screen API cannot be used.
• The audio track is pulled out of the mp4, decoded in WebAssembly by a vendored decoder, and played from a separate audio element kept in step with the video's play, pause, seek and speed. The video stays muted while that audio is in charge, so doubled sound is impossible on a host that can decode natively.

Recordings / Screenshots

Before

After