Video Subject Viewer: Accessibility of custom video controls

[goplayoutside3]

Package

lib-classifier

Is your feature request related to a problem? Please describe.

Stemming from PR #3684's discussion, the custom video controls built for video subject + drawing tools need accessibility upgrades.

• Use of spacebar or 'Enter' key while focused on the play/pause button - Behavior is sometimes delayed, but should play/pause the video instantaneously.
• Using left/right keys while focused on the select slider should step the video backwards and forwards.
• Keyboard use while focused on the select slider should match that of native browser controls, including the ability to press spacebar or 'Enter' in order to play/pause the video.
• Keyboard use while focused on the volume slider: the up and down arrows should increase and decrease the volume.

Describe the solution you'd like

See PR #3684's discussion for a few ideas on how to address the accessibility points above.