[share] Present share sheet on the view controller currently visible

[sianxz]

Description

Motivated by - and fixes - flutter/flutter#67103.

Related Issues

flutter/flutter#67103

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

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

• No, this is not a breaking change.

[stuartmorgan-g]

Thanks for the submission! However, we’re currently not accepting non-critical PRs for this plugin, as we hope in time to be able to transition users to the corresponding plugin in the Flutter Community Plus Plugins repository. We encourage you to submit your PR there.

We apologize for the long delay in triaging this PR. We’re in the process of overhauling our PR triage system to respond much more quickly, as well as working through the backlog.