Create separate regions for CEA608 rows

[felix-hoc]

Description

Issue: PW-22216

Problem

For CEA-608 captions, the “window color” + “window opacity” affect the whole subtitle overlay, blocking the view on the content.

Changes

• create separate region components for CEA-608 rows
• the absolute vertical position is now assigned to each row / region
  • as CEA-608 has exactly 15 rows, this is pre-calculated in CSS
• the actual cues are no longer positioned absolute-ly, and only hold the left offset

Checklist (for PR submitter and reviewers)

• CHANGELOG entry

[bitmovin-kenny]

Looks good even with two CEA Caption tracks active at the same time.