Fix generated wrapper for nested struct with static fn, alternative PR

[adetaylor]

Tests PR #1380 which for some reason didn't run tests.

[roife]

I just encountered an unusual issue on main branch that's preventing me from testing on my machine: when I run cargo run in the demo, I get the following error:

error[E0599]: no method named `describe` found for struct `Pin<Box<root::Goat>>` in the current scope
  --> demo/src/main.rs:23:14
   |
23 |         goat.describe().as_ref().unwrap().to_string_lossy(),
   |         -----^^^^^^^^--
   |         |    |
   |         |    this is an associated function, not a method
   |         help: use associated function syntax instead: `root::Goat::describe()`
   |
   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
note: the candidate is defined in an impl for the type `root::Goat`
  --> /Users/roife/code/autocxx/target/debug/build/autocxx-demo-a2dd4b564c10039d/out/autocxx-build-dir/rs/autocxx-ffi-default-gen.rs:1:1542
   |
1  | ...orward declaration. If you're sure it didn't, then you may be able to solve this by using instantiable!."] fn describe (_uhoh : autocxx :: BindingGenerationFailure) { } pub fn new () -> impl autocxx :: moveit :: new :: New < Output = Self > { unsafe { autocxx :: moveit ::...
   |                                                                                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0599`.

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UPDATE: This could be due to the issue that libc++ and autocxx do not work well together yet.