Add Upgrade Status module to core

Problem/Motivation

Since Drupal 8 was released, future major version upgrades should not be a big deal ;)
Drupal 9 (aka Drupal 8.9) will be the first time we'll see it happen and special guides were created → to help everyone experience a smooth process.

But it wouldn't feel like a smooth process until we can streamline the upgrade path to future major versions (Drupal 10, 11, etc.)

Proposed resolution

Add Upgrade Status module into core and enable it as part of a standard Drupal installation.

Tracking what's the latest deprecated functions as a preparation for next Drupal major release, should be as easy as tracking new updates in core and contrib modules. Keeping Drupal modules and custom code becomes an ordinary part of maintaining the life cycle of a website.

Additional benefits:

• It will be one less step (downloading/installing this module) that website maintainers need to worry about.
• It will bring more awareness to many more people (who don't have that knowledge without installing this module)
• It will allow a constant flow of updates to custom and contrib modules, as opposed to rushing to get everything ready just before to next major release is coming out.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet