cogl-shader: Prepend boilerplate for portable shaders

We now prepend a set of defines to any given GLSL shader so that we can
define builtin uniforms/attributes within the "cogl" namespace that we
can use to provide compatibility across a range of the earlier versions
of GLSL.

This updates test-cogl-shader-glsl.c and test-shader.c so they no longer
needs to special case GLES vs GL when splicing together its shaders as
well as the blur, colorize and desaturate effects.

To get a feel for the new, portable uniform/attribute names here are the
defines for OpenGL vertex shaders:

 #define cogl_position_in gl_Vertex
 #define cogl_color_in gl_Color
 #define cogl_tex_coord_in  gl_MultiTexCoord0
 #define cogl_tex_coord0_in gl_MultiTexCoord0
 #define cogl_tex_coord1_in gl_MultiTexCoord1
 #define cogl_tex_coord2_in gl_MultiTexCoord2
 #define cogl_tex_coord3_in gl_MultiTexCoord3
 #define cogl_tex_coord4_in gl_MultiTexCoord4
 #define cogl_tex_coord5_in gl_MultiTexCoord5
 #define cogl_tex_coord6_in gl_MultiTexCoord6
 #define cogl_tex_coord7_in gl_MultiTexCoord7
 #define cogl_normal_in gl_Normal

 #define cogl_position_out gl_Position
 #define cogl_point_size_out gl_PointSize
 #define cogl_color_out gl_FrontColor
 #define cogl_tex_coord_out gl_TexCoord

 #define cogl_modelview_matrix gl_ModelViewMatrix
 #define cogl_modelview_projection_matrix gl_ModelViewProjectionMatrix
 #define cogl_projection_matrix gl_ProjectionMatrix
 #define cogl_texture_matrix gl_TextureMatrix

And for fragment shaders we have:

 #define cogl_color_in gl_Color
 #define cogl_tex_coord_in gl_TexCoord

 #define cogl_color_out gl_FragColor
 #define cogl_depth_out gl_FragDepth

 #define cogl_front_facing gl_FrontFacing

cogl/cogl-shader-private.h

@@ -40,12 +40,17 @@ struct _CoglShader
 {
   CoglHandleObject   _parent;
   GLuint             gl_handle;
+  int                n_tex_coord_attribs;
   CoglShaderType     type;
   CoglShaderLanguage language;
+  char              *source;
 };
 
 CoglShader *_cogl_shader_pointer_from_handle (CoglHandle handle);
 
+void
+_cogl_shader_compile_real (CoglHandle handle, int n_tex_coord_attribs);
+
 CoglShaderLanguage
 _cogl_program_get_language (CoglHandle handle);