wined3d: Rewrite shader_glsl_lrp() to properly take the write mask into account, use the GLSL mix instruction.

In case of writing to an address register round the source.

wined3d: Move WINED3DSIO_SGE & WINED3DSIO_SLT from shader_glsl_map2gl() to shader_glsl_compare() where they belong.

Properly take the write mask into account

The write mask can only be one of .x, .y, .xy

gl_FogFragCoord and gl_PointSize are floats rather than vec4s in GLSL,
so they shouldn't have a destination swizzle, and the write mask we
return should consist of only the first component.

wined3d: Split shader_glsl_add_param() in shader_glsl_add_src_param() and shader_glsl_add_dst_param().

Thanks to Rob Shearman for noticing this.