[Feat] (Diligent): add dynamic vertex buffer upload path

DiligentRenderer can now upload arbitrary vec2 vertex data into a dynamic
vertex buffer and draw it with the existing triangle PSO. The local sanity
test uses this path instead of the hardcoded triangle, verifying buffer
basics on Turnip Adreno 750.

MobileGL/MG_Backend/Diligent/Renderer/DiligentRenderer.h

@@ -42,6 +42,7 @@ namespace MobileGL::MG_Backend::DiligentBackend {
         Bool Initialize(Uint32 width, Uint32 height);
         void Clear(Float r, Float g, Float b, Float a);
         void DrawTriangle();
+        void DrawVertices(const Float* vertices, Uint32 vertexCount);
         void ReadPixels(Uint32 x, Uint32 y, Uint32 width, Uint32 height, void* pixels);
         void Present();