v3.0.0 of cupertino_http

A macOS/iOS Flutter plugin that provides access to the Foundation URL Loading System.

Changelog excerpt:

• BREAKING CHANGE:Remove shouldUseExtendedBackgroundIdleModefrom URLSessionConfiguration.
• Support usage in Dart SDK projects.
• Fix a bug where close reasons not containing valid UTF-8 would cause an uncatchable exception to be thrown.
• Exclude unnecessary generated code. Slightly reduces disk space requirements.
• Add URLSessionTask.taskDelegatesetter and URLSessionTask.delegatebuilder to enable use of task-level delegates.
• BREAKING:Update minimum supported versions to iOS […]