BLF/OpenGL: draw text with new immediate mode

Part of T49043

source/blender/gpu/shaders/gpu_shader_text_vert.glsl

@@ -1,20 +1,24 @@
 
-// TODO(merwin):
-// - uniform color, not per vertex
-// - generic attrib inputs (2D pos, tex coord)
+uniform mat4 ModelViewProjectionMatrix;
 
 #if __VERSION__ == 120
-  flat varying vec4 color;
-  noperspective varying vec2 texcoord;
+  attribute vec2 pos;
+  attribute vec2 texCoord;
+  attribute vec4 color;
+  flat varying vec4 color_flat;
+  noperspective varying vec2 texCoord_interp;
 #else
-  flat out vec4 color;
-  noperspective out vec2 texcoord;
+  in vec2 pos;
+  in vec2 texCoord;
+  in vec4 color;
+  flat out vec4 color_flat;
+  noperspective out vec2 texCoord_interp;
 #endif
 
 void main()
 {
-	gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
+	gl_Position = ModelViewProjectionMatrix * vec4(pos, 0.0, 1.0);
 
-	color = gl_Color;
-	texcoord = gl_MultiTexCoord0.st;
+	color_flat = color;
+	texCoord_interp = texCoord;
 }