avm2: Implement UVT-mapped bitmap triangles across render backends and move triangles outside tassellation

[wsxarcher]

Description

This PR makes AVM2 Graphics.drawTriangles and GraphicsTrianglePath first-class indexed triangle primitives. Vertices, indices, UV/UVT data, and culling are validated before rendering, while bounds, hit testing, active fill state, and Flash’s independent-triangle winding behavior are preserved.

Triangles now bypass Lyon tessellation and are uploaded directly across Canvas, WebGL, and WGPU. WebGL and WGPU use dedicated UVT vertex layouts and perspective-correct homogeneous interpolation without increasing ordinary shape vertex sizes; Canvas computes a bitmap transform per triangle. Unit and visual coverage includes UV/UVT conversion, invalid data, winding, drawing state, hit testing, and bitmap mapping.

Fixes #17639

Checklist

• I, a human, have self-reviewed this PR and fully understand the changes within.
• I have made or updated tests where possible.
• All of my commits are properly scoped, compile successfully, and pass all tests.
• This PR does not make sense to split up into smaller PRs.
• An LLM was involved in the authoring of this code.

[kjarosh]

Have you looked into the following?

• render: Skip tessellation when drawing triangles #23819
• avm2: Implement Graphics.drawTriangles with UVT data #16950

[wsxarcher]

Only the second one and took inspiration as I thought it was abandoned, the focus was making the game work. Did not know about the first PR, but I can wait to rebase if there is an ongoing refactor.

[kjarosh]

The second one mentions the issue: triangles probably should not go through tessellation. Triangles in Flash Player behave differently compared to drawn shapes (cf. unfinished strokes/fills), and in addition, it doesn't make sense to tessellate triangles in general, as they are primitive shapes and the point of using them is performance in the first place.

[wsxarcher]

You are right, now it has a new drawing command just for triangles like your draft and I added the tests from the old PR