scripts: include function versions in API definition

scripts: include function versions in API definition

In order to auto-generate more of the language binding code, it is
desirable to know what libvirt version an API was introduced in.
We can extract this information from the .syms files and expose
it in the API description

eg instead of

  <function name='virNodeNumOfDevices' file='libvirt-nodedev'
            module='libvirt-nodedev'>

we now have

  <function name='virNodeNumOfDevices' file='libvirt-nodedev'
            module='libvirt-nodedev' version='0.5.0'>

This will benefit this proposal:

  https://gitlab.com/libvirt/libvirt-go-module/-/merge_requests/7

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Tested-by: Victor Toso <victortoso@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>