Add facingMode constraint configuration to Jason (#27)

[evdokimovs]

Part of #27

Synopsis

We need to configure exact or ideal MediaTrackConstraints.facingMode constrain.

Solution

Add MediaTrackConstraints.facingMode configuring to the DeviceVideoTrackConstraints.

Checklist

• Created PR:
  • [x] In draft mode
  • [x] Name contains Draft: prefix
  • [x] Name contains issue reference
  • [x] Has k:: labels applied
  • [x] Has assignee
• [x] Documentation is updated (if required)
• [x] Tests are updated (if required)
• [x] Changes conform code style
• [x] CHANGELOG entry is added (if required)
• [x] FCM (final commit message) is posted
  • [x] and approved
• [x] Review is completed and changes are approved
• Before merge:
  • [x] Milestone is set
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  • [x] Draft: prefix is removed
  • [x] All temporary labels are removed

[evdokimovs]

FCM

Add facingMode constraint configuration to Jason (#137, #27)

- add FacingMode enum
- add DeviceVideoTrackConstraints::ideal_facing_mode and DeviceVideoTrackConstraints::exact_facing_mode methods
- add 'Facing user' and 'Facing environment' video devices to 'e2e-demo' and 'demo'