Audit CanvasViewPosition

[JPMeehan]

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• Audit all uses of CanvasViewPosition and determine when fields are always filled in. This is probably just in canvasPan (if at all).
• Rename CanvasViewPosition to Canvas.ViewPosition or possibly Canvas.View which is how it was named in an older version.

Broad note: Complex types should always be factored out to make it easier for downstream consumers.