`ImageCollectionEditor` unable to add an image at runtime

[RussKie]

• .NET Core Version: (e.g. 3.0 Preview1, or daily build number, use dotnet --info)
• Have you experienced this same bug with .NET Framework?: Yes/No

Problem description:

Having ported ImageCollectionEditor code from NETFx, it appears impossible to add an image at run-time via ImageCollectionEditor.
The error appears in both NET Fx (4.7.2/4.8) and NET Core implementations.

It is however possible to add an image via the editor at design-time.
I've checked the VS implementation and it also appears to be the same as in latest NET Fx.

Relates to #1273

Actual behavior:

• to a dynamically created ImageList:
  

• to an ImageList created at the design time
  

Expected behavior:

It is possible to add an image at run-time

Minimal repro:

RussKie/Test-ImageCollectionEditor#1

[RussKie]

@merriemcgaw @dreddy-work

@Olina-Zhang could you please check whether this ever worked in NET Fx?

[Olina-Zhang]

@RussKie I checked all .Net frameworks, behaviors are same, at VS design time, it can add image successfully, and in PropertyGrid runtime, there is an error existed when adding image in ImageCollectionEditor:

[RussKie]

Thank you, @Olina-Zhang.

It will be fixed in Core. @merriemcgaw what's our appetite getting it fixed in NETFx?

[merriemcgaw]

If we have a customer requesting the fix we likely would, but really not until then.