fix layout specification for blend equations and add sample shading due to some impls needing it

Author: HeliumAnt

Data/Base.rte/Shaders/Background.frag

@@ -1,14 +1,14 @@
 #version 330
 #extension GL_KHR_blend_equation_advanced: enable
+#extension GL_ARB_sample_shading: enable
 
 in vec2 textureUV;
 in vec4 vertexColor;
 
 #ifdef GL_KHR_blend_equation_advanced
-layout(blend_support_all_equations) out vec4 FragColor;
-#else
-out vec4 FragColor;
+layout(blend_support_all_equations) out;
 #endif
+out vec4 FragColor;
 uniform sampler2D rteTexture;
 uniform sampler2D rtePalette;
 uniform vec4 rteColor = vec4(1.0);