Add DebuggerTypeProxy for ListDictionaryInternal

[JamesNK]

This PR added debugger display to ListDictionaryInternal. A DebuggerTypeProxy should also be added to improve displaying the collection's contents.

The current display in VS:

For example:

runtime/src/libraries/System.Private.CoreLib/src/System/Collections/ArrayList.cs

Lines 2640 to 2653 in 86252f7

	internal sealed class ArrayListDebugView
	{
	private readonly ArrayList _arrayList;
	public ArrayListDebugView(ArrayList arrayList)
	{
	ArgumentNullException.ThrowIfNull(arrayList);
	_arrayList = arrayList;
	}
	[DebuggerBrowsable(DebuggerBrowsableState.RootHidden)]
	public object?[] Items => _arrayList.ToArray();
	}

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Issue Details

---

This PR added debugger display to ListDictionaryInternal. A DebuggerTypeProxy should also be added to improve displaying the collection's contents.

The current display in VS:

For example:

runtime/src/libraries/System.Private.CoreLib/src/System/Collections/ArrayList.cs

Line 2640 in 86252f7

internal sealed class ArrayListDebugView

Author:	JamesNK
Assignees:	-
Labels:	area-System.Collections, untriaged
Milestone:	-

[tarekgh]

@arturek are you interested to submit a PR for this one too?

[arturek]

@tarekgh yes, thanks. I wrote the code, but I cannot find ListDictionaryInternal's unit tests.

[tarekgh]

@arturek ListDictionaryInternal is an internal thingy, so I don't think we have unit tests for it. Can't you test it through the Exception class? or add new tests for it if needed.