[WIP] Autogenerate libvirt enum typings

This is the initial work for autogenerating the enum typings using directly the C's libvirt code. #3 (moved)

Note: this code adds dependencies to the library:

• github.com/dave/jennifer/jen
• github.com/alecthomas/participle

Maybe we should add go modules support?

Missing items:

• Use the generated typings in the existing types instead of using strings
• Ensure all the enums are generated
• ? Generate only the necessary typings for libvirt-go-xml
• Document the code generation and ensure it's always generated