Auto-resize dialogs when resizing windows

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

One thing that I run into every now and then is that I have a small app window, open a file dialog, and then resize the app window for a bigger dialog, but it stays at the initial size.

Related: https://github.com/fyne-io/fyne/issues/3917

Is it possible to construct a solution with the existing API?

No.

Describe the solution you'd like to see.

It would be nice if dialogs would scale with the window size, maybe using a percentage for sizing.