D3D12: Add Quad integration test with texture sampling

- Add quad test that renders a textured quad with earth texture
- Add quad.hlsl shader with texture sampling (Texture2D + SamplerState)
- Add SRV descriptor heap and root signature with SRV table
- Fix MessageBox errors -> Log() console output
- Fix shader float2->float4 type mismatch
- Fix texture initialization to use proper command list handling
- Add shader error output to stderr in D3D12Shader
- Add Map error logging in D3D12Screenshot

tests/RHI/D3D12/integration/quad/Res/Shader/quad.hlsl

@@ -0,0 +1,23 @@
+struct Vertex {
+    float4 pos : POSITION;
+    float4 texcoord : TEXCOORD0;
+};
+
+struct VSOut {
+    float4 pos : SV_POSITION;
+    float4 texcoord : TEXCOORD0;
+};
+
+VSOut MainVS(Vertex v) {
+    VSOut o;
+    o.pos = v.pos;
+    o.texcoord = v.texcoord;
+    return o;
+}
+
+Texture2D T_DiffuseTexture : register(t0);
+SamplerState samplerState : register(s0);
+
+float4 MainPS(VSOut i) : SV_TARGET {
+    return T_DiffuseTexture.Sample(samplerState, i.texcoord.xy);
+}