Implement View Transitions feature plugin

[felixarntz]

This is a follow up issue to #1963, with the purpose to track the actual implementation of the new View Transitions feature plugin up until the initial launch.

The work will be broken down into a few iterative PRs to ease review and discussion. Here's the list:

• Foundation (add_theme_support, opt in to view transitions via CSS) (Scaffold View Transitions feature plugin #1998)
• Add support for specifying global transition names and post transition names (Add support for dynamic view transition names for global elements, and certain post elements to View Transitions plugin #1999)
• Add support for different animations
• Add settings UI to control animations, global transition names, and post transition names
• Add support for chronological and pagination transitions
• Mark plugin as ready to launch and include in Performance Lab
• Publish first version on WordPress.org

The implementation of all these PRs will be based on WordPress/wordpress-develop#8370 and heavily reuse the code from that experimental Core PR. The main difference will be the inclusion of settings to control via UI, plus adjustments to satisfy requirements of implementing as a plugin.