Refactor WeakRefCollection to replace ArrayList with List<T>

[elachlan]

Related: #8140

Microsoft Reviewers: Open in CodeFlow

[elachlan]

@halgab could you please give this a quick review?

[halgab]

Happy to help!
I just see a minor potential improvement.

I don;t know if you've noticed, but this type is also defined here. I don't know if code consolidation between the winforms projects and System.Drawing.Common is something that should be considered, knowing that the latter targetting netfx makes it less profitable.

Other open questions I have about this type (but that are outside the scope of this PR):

• should this be made generic?
• if that's the case, should we be using WeakReference<T> under the hood? And more generally should we try and replace WeakReference with its generic counterpart across codebase?

[halgab]

Suggested change

	get => InnerList[index] is WeakRefObject weakRef && weakRef.IsAlive ? weakRef.Target : null;
	get => InnerList[index].Target;

According to the WeakReference docs, Target returns null if IsAlive is false

[JeremyKuhne]

@elachlan I don't think there is any real difference between the two WeakRefCollection classes. Presuming they are the same, it would be worth merging to Common and linking into both projects.

It would also be worth looking at whether these can be typed. Can this be WeakRefCollection<T>? And more correctly: WeakReferenceList<T> : IList<T>??

[elachlan]

@JeremyKuhne what namespace do you want me to use if we merge them?

[JeremyKuhne]

what namespace do you want me to use if we merge them?

@elachlan you can just put this in System.Collections or System.Collections.Generic if you make it of T. (As it is internal)

[elachlan]

Closing in favor of #10291