docs(package_info_plus): Add platform specific documentation

[miquelbeltran]

Description

• Adds platform specific documentation to the different package properties.

Related Issues

• Closes [Bug]: It's not clear what appName actually means on desktop platforms #2842

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.

[Hixie]

Thanks!