Add drawTriangle engine function

[ItzAditya43]

Closes #38

Adds a drawTriangle(...) engine function, following the three-part structure described in the issue.

Changes

• ArcadeMaker.Core/IGame.Funcs.cs — declaration with [EngineFunc] / [Param] attributes.
• Engines/MonoGame/Core/ArcadeMakerMonoGame.cs — MonoGame implementation.
• ArcadeMaker.IDE/Debugging/FutileGame.cs — futile implementation.

Usage

drawTriangle(x1, y1, x2, y2, x3, y3)                    // outlined, thickness 1
drawTriangle(x1, y1, x2, y2, x3, y3, false)             // filled
drawTriangle(x1, y1, x2, y2, x3, y3, true, 3)           // outlined, thickness 3

Two notes / questions

1. Optional outline and thickness

The issue suggested [EngineFunc(7)] with a required outline. I used [EngineFunc(6, 7, 8)] instead, so that the signature mirrors the neighbouring drawRect / drawEllipse, which both take their 4 coordinates plus an optional outline and an optional thickness:

[EngineFunc(4, 5, 6)]   // drawRect / drawEllipse
[EngineFunc(6, 7, 8)]   // drawTriangle

This keeps the primitive-drawing functions consistent with each other, and defaults to an outline like the others do. Happy to change it back to a strict 7 parameters if you'd prefer to stay with the issue's signature.

2. Filled triangles

MonoGame.Extended's ShapeExtensions gives SpriteBatch a DrawPolygon(...) for outlines, but the only solid helper it exposes is FillRectangle(...) — there is no filled-polygon method on SpriteBatch (DrawSolidPolygon lives on VectorDraw.PrimitiveDrawing, which needs its own PrimitiveBatch).

Rather than throw for the filled case (as drawEllipse currently does), I filled the triangle by rasterizing it as a series of horizontal scanlines, each drawn with FillRectangle. It stays inside the existing SpriteBatch pass, so it needs no extra graphics state or render-target juggling.

If you'd rather introduce a PrimitiveBatch and get a single-draw-call filled polygon out of it, that would be more efficient for large triangles and would let drawEllipse be filled too — but it felt like a bigger change than this issue called for, so I kept it self-contained. Let me know if you'd prefer that direction.

Feedback very welcome — this is my first contribution here.

[ArcadeMakerSources]

Hey, thank u very much! 🙏🏼
I think that filling the triangle by rendering multiple rectangles might be problematic in performances. Throwing (like in the ellipse func) would be better for now, for my mind.
Also, I want to keep this project non AI as much as possible. I know that this is how modern programming works, but still, I want to make this project a bit retro in both the product it becomes and the way it is developed. I hope you're fine with that, and I would really love to see you keep contributing with hand-written code, if you are interested 🙂
Anyway, i won't have access to my pc for a few days now, so just know that it will take me some time to review and approve this PR