[shared_preferences] Add shared preferences devtools

[adsonpleal]

This PR adds the shared_preferences_tools package. This package user the devtools_extension tooling to create a tool for shared preferences. The idea of this PR came from @kenzieschmoll on this issue. Initially I've published this tool as a separate package, but this PR aims to bring the functionality to the main shared_preferences package. Once this PR gets merged I'll archive the shared_preferences_tools package.

https://github.com/flutter/packages/assets/11666470/fcf71145-c330-4397-b62e-c0c4c8bc9f01

Pre-launch Checklist

• [X] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [X] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [X] I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• [X] I signed the CLA.
• [X] The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• [X] I linked to at least one issue that this PR fixes in the description above.
• [X] I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• [X] I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• [X] I updated/added relevant documentation (doc comments with ///).
• [X] I added new tests to check the change I am making, or this PR is test-exempt.
• [X] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.