d3d11: Implement d3d11_input_layout_to_wined3d_declaration() on top of vkd3d_shader_parse_input_signature().

This was originally prompted by the fact that
wined3d_extract_shader_input_signature_from_dxbc() allocates elements with
HeapAlloc(), but d3d11_input_layout_to_wined3d_declaration() attempts to free
them with free(). That's a regression introduced by commit
b951c37b. Since we're touching the code
though, we may as well use vkd3d_shader_parse_input_signature(), and get rid
of wined3d_extract_shader_input_signature_from_dxbc().