Fix: MessageBox does not support WindowStartupLocation

[textGamex]

Pull request type

Please check the type of change your PR introduces:

• [ ] Update
• [x] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation content changes

What is the current behavior?

The MessageBox will only display in the center of the screen, and the WindowStartupLocation is not effective.

Issue Number: #1045

What is the new behavior?

• fix this bug.

Other information

Using reflection to invoke a private property of the Window class to help determine if the MessageBox can be displayed centered on the Owner.

In the .NET 8 assembly, I utilized UnsafeAccessor to enhance performance.