[Swift6]: Use @State over @StateObject in ViewContext

[ra1028]

Checklist

• Reviewed the README and documentation.
• Checked existing issues & PRs to ensure not duplicated.

Description

@StateObject is slightly less performant than @State due to the overhead of resubscribing the subtree's ObservableObjects when updating the parent view.
However, Swift5's actor isolation inference seems to have a special behavior when using @StateObject (views that depend on @ViewContext indirectly through other dynamic properties are not isolated to the main actor), and I found out that it breaks backward compatibility.
Most likely it's a bug, but fortunately the actor isolation inference for property wrapper will be removed in Swift6, so then we can replace state management using @StateObject with @State.

Example Use Case

N/A

Alternative Solution

No response

Proposed Solution

No response

Motivation & Context

No response

[ra1028]

This problem disappears when the experimental flag StrictConcurrency is enabled, and all views that directly or indirectly depend on the ViewContext are isolated to the MainActor, so it still seems to be a bug.

[ra1028]

close #151