Added deconstructors to the primitives

[synercoder]

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Description

I added deconstructors to the primitives. I was trying to use ImageSharp for a project, and when using the mutate function I already had a variable named size.

So then I wanted to use a deconstructor and I tried:

var (width, height) = ctx.GetCurrentSize(); 

This proofed not possible since there were no deconstructors, so I thought I write a few.

With this PR the above code will work, and makes imagesharp a bit more usable :)

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[JimBobSquarePants]

Will review this tonight.

[JimBobSquarePants]

This all looks great to me. Thanks for your help!