Fix sharing not working on iOS 18

[gaucidaniel]

On the latest version, the library does not work on iOS 18 as discussed here. This pull requests updates the ShareHandlerIosViewController to fix this issue while maintaining compatibility with older versions of iOS. Until this PR is merged, it can be tested by updating your pubspec.yaml to include the following:

dependency_overrides:
  share_handler_ios:
    git:
      url: https://github.com/gaucidaniel/share_handler.git
      path: share_handler_ios
      ref: main