Notice that I'm using floats instead of doubles in the new function,
mostly to be able to use struct wined3d_matrix and multiply_matrix().
At a rough estimate the precision should still be good enough.

While these won't be used by the shader, they potentially affect the
calculated offset for WINED3D_APPEND_ALIGNED_ELEMENT elements.

Instead of a fixed array of wined3d_shader_signature_element structures.
Shader model 4 shaders can have different semantics in a single
register, e.g.  v1.xy TEXCOORD0 and v1.zw TEXCOORD1, so having a single
wined3d_shader_signature_element structure per register isn't
necessarily sufficient.