Cherry-pick from #14198 to break it down into smaller chunks.

Purpose

This is a follow-up PR on the package integration PR. It builds on the continuous design guides as per this Figma link.

Even though a lot of areas have been improved, this is still work in progress. With the main skeleton of the solution in place, the major directions of work are:

• design changes in Search for packages tab
• design changes in Publish a package tab
• design changes in My packages tab
• design changes in Publish version tab

Screenshots

01 loading screen

02 discard loading timeout

03 package details extension interaction

04 package manager contents

05 package manager to preferences interaction

Declarations

Check these if you believe they are true

• The codebase is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning and are documented in the API Changes document.
• This PR modifies some build requirements and the readme is updated
• This PR contains no files larger than 50 MB

Release Notes

Progression work on the Package Manager

• interactions between different parts of the package manager and between package manager and preferences screen
• added empty, loading, idle screens
• work on the PacakgeDetailsExtension to allow hosting inside the PackageManager
• misc refactor

Reviewers

@reddyashish
@QilongTang

FYIs

@Amoursol