Add explicit padding fields in the corresponding structures.

This is similar to 0bdab5f8.

d3d9: Use separate codepaths for failure and NULL return values in GetVertexShader() / GetPixelShader().

It's only used for shader_hw_map2gl() and vshader_hw_rsq_rcp(), and we
can handle those the same way we handle the GLSL equivalents.

widl: Write the local stubs file based on the parsed list of statements, rather than using hooks in the parser code.

widl: Write the generated file containing IID, DIID, CLSID and LIBID data based on the parsed list of statements instead of using hooks in the parser code.