Add BitmapContext extension methods for direct drawing operations

[Copilot]

This PR adds extension methods for the BitmapContext class that allow users to perform drawing operations directly on a BitmapContext instead of having to go through the WriteableBitmap. This enables more efficient code when doing multiple drawing operations since the BitmapContext only needs to be created once.

Key changes

• Created a new BitmapContextExtensions class with extension methods that mirror existing WriteableBitmap extension methods
• Implemented drawing methods: lines, rectangles, ellipses
• Implemented fill methods: rectangles, ellipses
• Implemented blit operations for copying pixels between contexts
• Implemented transform operations (flip)
• Added the class to all relevant project files

Usage example

Before, users needed to use WriteableBitmap methods that create/dispose contexts internally:

varbmp=newWriteableBitmap(500,500);// Each call creates and disposes a BitmapContext internallybmp.DrawLine(10,10,100,100,Colors.Red);bmp.DrawRectangle(50,50,150,150,Colors.Blue);bmp.FillEllipse(200,200,300,300,Colors.Green);

Now, users can reuse the same context for multiple operations:

varbmp=newWriteableBitmap(500,500);// Create the context onceusing(varctx=bmp.GetBitmapContext()){// Multiple drawing operations using the same contextctx.DrawLine(10,10,100,100,Colors.Red);ctx.DrawRectangle(50,50,150,150,Colors.Blue);ctx.FillEllipse(200,200,300,300,Colors.Green);}// Context is disposed only once

This provides better performance when doing many consecutive drawing operations, especially in loops, and also allows users to perform drawing operations from multiple threads.

Fixes#92.

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[reneschulte]

@epsi1on Can you take a look if these are the wrappers and interfaces you had in mind?

[epsi1on]

Seems yes, but not completely.
What i had in mind was to simply replace all extensions of WritebaleBitmap into extensions of BitmapContext. (as stated in #76 and maybe other issues).

Although the BitmapContext does not allocated every time bmp.GetBitmapContext() is called (because a caching mechanism is there), but this would make it a little more robust I think.

If you are OK with this idea, I can make a pull request.

Thanks

[epsi1on]

Instead of replacing all extension methods of WriteableBitmap, there could be an identical copy which accepts BitmapContext instead:

original code:

publicstaticvoidDrawLineAa(thisWriteableBitmapbmp,intx1,inty1,intx2,inty2,intcolor,Rect?clipRect=null){//actual pixel manipulation code here}

new code:

publicstaticvoidDrawLineAa(thisWriteableBitmapbmp,intx1,inty1,intx2,inty2,intcolor,Rect?clipRect=null){using(varctx=bmp.GetBitmapContext())DrawLineAa(ctx,x1,y1,x2,y2,color,clipRect);}publicstaticvoidDrawLineAa(thisBitmapContextctx,intx1,inty1,intx2,inty2,intcolor,Rect?clipRect=null){//actual pixel manipulation code here}