[MDI] Add possibility to align minimized child to default location (TOP LEFT)

Is your feature request related to a problem? Please describe. WinForms override standard MDI behavior without option to use original one. It’s lead to all child windows layout (with minimized windows) are mess up after main window resize. This can happened after simple resize, or after resolution changed (for example if your connect by rdp from other device), etc… before res. change (left - WinForms, right - MFC): after res. change (left - WinForms, right - MFC):

Video:

https://user-images.githubusercontent.com/17767561/112429754-26a14200-8d4e-11eb-83d5-393626ad23b6.mp4

For now we need to manually revert this move (with same technique) after each resize 😦

Draft API Proposal

• Will this feature affect UI controls? Yes.
• Will VS Designer need to support the feature? If yes, describe how you expect it to funсtion. Yes - Form will have a new property in PropertyGrid
• What impact will it have on accessibility? No.
• Will this feature need to be localized or be localizable? Yes.

We need to add bool property to Form class, let it be MdiChildrenMinimizedAnchorTop:

namespace System.Windows.Forms
{
    public partial class Form : ContainerControl
    {
        /// <summary>
        /// true - anchoring minimized MDI children to the TopLeft of the parent form (windows default). false - anchoring minimized MDI children to the BottomLeft of the parent form (WinForms default)
        /// </summary>
        [SRCategory(nameof(SR.CatWindowStyle))]
        [DefaultValue(false)]
        [SRDescription(nameof(SR.FormMdiChildrenMinimizedAnchorTopDescr))]
        public bool MdiChildrenMinimizedAnchorTop { get; set; }
    }
}

To do.

1. Discuss a name for the property.
2. Discuss a description for the property. Translations?
3. Category: Style or may be Layout?
4. Implement trivial logic with this property in SetBoundsCore method of MdiClient class and do PR.

[terrajobst]

Easiest is to file an issue in the winforms repo, put it in the 6.0.0 milestone, mark it as blocking and api-ready-for-review. We’ll look at it first thing Tuesday morning then.

[merriemcgaw]

We are looking for someone to propose (and implement) an API that would enable this to happen. It has to go through the full API review process, and we can help a bit with that. But it looks like there are more urgent fires to fight for .NET 6 so it doesn’t look like we will have the resources to enable this feature just yet. If the community can, that would be something we’d totally take.