Refactor DesignerHost to replace ArrayList with List<T>

[elachlan]

Related: #8143, #8357

Microsoft Reviewers: Open in CodeFlow

[elachlan]

I made some more changes designed to avoid problems when an array is passed in and not a list/arraylist. Also fixed a caller to the method which was passing in an arraylist.

[elachlan]

@dreddy-work is the test failure a flaky test?

[dreddy-work]

Error message
System.NullReferenceException : Object reference not set to an instance of an object.

Stack trace
   at System.Windows.Forms.Tests.ListViewLabelEditAccessibleObjectTests.ListViewLabelEditAccessibleObject_IsPatternSupported_ReturnsExpected() in /_/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ListViewLabelEditAccessibleObjectTests.cs:line 67
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr)

[dreddy-work]

@dreddy-work is the test failure a flaky test?

Only on ARM suggests so. @dmitrii-drobotov can you check why accessible object is disposed in this case?

[dmitrii-drobotov]

@dreddy-work is the test failure a flaky test?

Only on ARM suggests so. @dmitrii-drobotov can you check why accessible object is disposed in this case?

The exception actually looks like that _labelEdit was null here for some reason:

winforms/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ListViewLabelEditAccessibleObjectTests.cs

Lines 66 to 67 in b0c7518

	ListViewLabelEditNativeWindow labelEdit = listView.TestAccessor().Dynamic._labelEdit;
	ListViewLabelEditAccessibleObject accessibilityObject = (ListViewLabelEditAccessibleObject)labelEdit.AccessibilityObject;

There is a condition when it may not be created, I assume cancelEdit was true, but it's hard to tell why:

winforms/src/System.Windows.Forms/src/System/Windows/Forms/ListView.cs

Lines 6484 to 6517 in b0c7518

	case (int)LVN.BEGINLABELEDITW:
	{
	Debug.Assert(_labelEdit is null,
	"A new label editing shouldn't start before the previous one ended");
	if (_labelEdit is not null)
	{
	_labelEdit.ReleaseHandle();
	_labelEdit = null;
	}
	bool cancelEdit;
	if (_blockLabelEdit)
	{
	cancelEdit = true;
	}
	else
	{
	NMLVDISPINFO* dispInfo = (NMLVDISPINFO*)(nint)m.LParamInternal;
	LabelEditEventArgs e = new(dispInfo->item.iItem);
	OnBeforeLabelEdit(e);
	cancelEdit = e.CancelEdit;
	}
	m.ResultInternal = (LRESULT)(nint)(BOOL)cancelEdit;
	_listViewState[LISTVIEWSTATE_inLabelEdit] = !cancelEdit;
	if (!cancelEdit)
	{
	_labelEdit = new ListViewLabelEditNativeWindow(this);
	_labelEdit.AssignHandle(PInvoke.SendMessage(this, (User32.WM)PInvoke.LVM_GETEDITCONTROL));
	}
	break;
	}

Should we create a new issue for it through Runfo? https://runfo.azurewebsites.net/search/tests/?q=started%3A%7E100+definition%3A76+name%3A%22system.windows.forms.tests.listviewlabeleditaccessibleobjecttests.listviewlabeleditaccessibleobject_ispatternsupported_returnsexpected%22

[dreddy-work]

#8682