Validate libraries.yml files

Problem/Motivation

In 📌 Add a deprecation support for library-overrides Active we introduced a new key in libraries.yml for backward compatibility.

In 📌 Move system/base component CSS to respective libraries where they exist Fixed we started to use that key in core, however there was an error in the syntax.

We should validate libraries.yml files in some way to prevent this happening again.

Steps to reproduce

Proposed resolution

Add assertions for various parts of the file as we read it?
Add a schema for libraries.yml and validate the files on load?
Add test coverage that ensures all files are valid?

Remaining tasks

Decide on the best method.

User interface changes

API changes

Data model changes

Release notes snippet