[VisualDiagnostics] Fix RectangleAdorner with updated math

[drasticactions]

Description of Change

The UITools team uses its own SelectorAdorner (Using IAdorner) for rendering its adorners used in Visual Studio. This was originally kept in line with the existing RectangleAdorner but as we updated the math in MAUI and our own code, this control was left broken.

This PR fixes that, and syncs the two again with the proper logic for render adorners on iOS, Android, Mac Catalyst, and Windows.

NOTE: The current Adorners drawn in Visual Studio using the Live Visual Tree or XAML Live Preview are not affected by this PR and should be currently working in MAUI. This is only for the built in RectangleAdorner.

Issues Fixed

Fixes #8727

[mattleibow]

I managed to fix this by simply not doing density calculations. Looking at the code, it appears you do 1/density and then later another /1/density which feels like you are working around the bug where you are not supposed to use density in the calculations at all.

The bounding box should be in scaled units and then you are to draw in scaled units.

[drasticactions]

@mattleibow I was syncing what we had in UI tools with it here, which I assumed was right.

I was wrong with that assumption then, or this is a conversation to have with @etvorun since I thought we did need to care about density. If you wanna fix this by removing the density calculation, you can do that and close this PR. I'm more than happy to have less code than more in this case.

[mattleibow]

I do not believe the logic is wrong, but what I do see is a bunch of division that ultimately ends up in a very similar place. I think this may be due to the fact that there was a bug in GA that used device pixels instead of scaled pixels. That required half the work in the IDE. Then we fixed that and then maybe the IDE did the other half instead of just using values directly.

In the screenshot below, we got the bounding box and then in the update model logic it converts it to device units then back to scaled units and then does some math. You can see the value of box (direct from the UI) is almost the same as the final model.BoundingBox:

Model	Direct

public virtual void Draw(ICanvas canvas, RectF dirtyRect)
{
	canvas.FillColor = FillColor;
	canvas.StrokeColor = StrokeColor;

	var boundingBox = VisualView.GetBoundingBox();

	DrawnRectangle = boundingBox.Offset(Offset); // <- direct usage

	canvas.FillRectangle(DrawnRectangle);
}

[etvorun]

@mattleibow this change is a fork of our WPF adorner logic. The only reason we need 1/density is to achieve pixel perfect 1px crisp lines (see use of RoundToPixels). Otherwise we use units only.