Description

This PR contains several improvements on the share_plus package:

• Unified the 3 static methods into a single non-static method.
• Access to SharePlus class via instance singleton, rather than using static methods.
• Allow to mock SharePlatform for testing.
• Consolidated the use of subject and title.
• Wrapped all share parameters into the ShareParams class.
• Unified native share implementations into a single method (when possible).
• Added mailToFallbackEnabled to disable web mailTo failback (enabled by default)
• downloadFallbackEnabled is no longer a static setting but part of the ShareParams
• Sharing uri is now supported on all platforms by sharing the URI as plain text

Not a breaking change, since the old API is still compatible, only it has been deprecated.
But we should consider bumping the version of share_plus to a major release nevertheless, since the deprecation will break CI/CD lint analysis.

TODO:

• Implement Linux
• Implement macOS
• Implement Android
• Implement iOS
• Implement Windows Native
• Implement Windows Fallback
• Implement Web
• Implement new tests
• Document public method

Related Issues

• Closes [Request]: share_plus refactor #3403
• Closes [Request]: (share_plus) EXTRA_TITLE in share Intent on Android #3307
• Closes [share]: make Share an instantiable object #2818

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.