fix(share_plus): Avoid crash on iOS during file and text sharing in add-to-app scenario

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Description

Fixes current active UIViewController passing to file and text sharing methods.

The error:

Attempt to present <UIActivityViewController: 0x1312eb600> on <Some.AnotherController: 0x10f713800> (from                           
  <Some.AnotherController: 0x10f713800>) which is already presenting <Some.ThirdController: 0x10f404000>. 

Related Issues

• Fixes [Bug]: Share Plus doesn't work with file and text sharing in Flutter add-to-app scenario #3737

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.

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Tests are passing locally.
There's some issue with downloading https://storage.googleapis.com/flutter_infra_release/flutter//engine_stamp.json. in analyze workflow. It's some global issue, we're experiencing this with our own pipelines as well but it's not stable, sometimes it works fine, need to rerun the pipeline