wined3d: Improve/implement D3DSIO_TEX.

- unify per-version cases into a single sequence
- make use of get_register_name() for the destination register
- ignore destination write mask - it's only allowed on 2.0+ shaders,
  and only the default mask is allowed there (xyzw)
- enable swizzle on texld 1.4 (it works together with dw/dz modifiers)
- implement for shaders 2.0-3.0