Import the vim module

In Vim, the vim module is always imported by magic in the global scope,
but the docs suggest that you're supposed to import it anyway.

In NeoVim it's never imported so we were relying on some other plugins
having already imported it.

autoload/vimspector/internal/state.vim

@@ -27,6 +27,7 @@ function! vimspector#internal#state#Reset() abort
     let prefix='neo'
   endif
     py3 << EOF
+import vim
 from vimspector import debug_session
 _vimspector_session = debug_session.DebugSession( vim.eval( 'prefix' ) )
 EOF