Support casting for Web

[hawk23]

Description

Adds support for Google Cast for Web.

Changes

• Platform abstraction for cast manager
• If cast manager has been initialized with options, set them on the player config to enable casting for the player instance
• Support for cast related events
• Support for sending custom messages to cast receiver

TODO

• Extend Casting example to show also value of isCasting and isCastAvailable
  • Done in: Add player info widget to Casting sample #202
• Optional: Refactor Casting example for simplicity
  • Done in: Add player info widget to Casting sample #202
• Manually test sendMessage for web

Checklist (for PR submitters and reviewers)

• 🗒 CHANGELOG.md entry for new/changed features, bug fixes or important code changes
• 🧪 Tests added and/or updated
• 📢 New public API is fully documented