[carp-header-parse] parse typedefs and generate corresponding `register-type` calls

[scolsen]

carp-header-parse doesn't yet support typedefs, but we can support it, and generate corresponding register-type calls.

For basic typedefs e.g. typedef int Foo; we can generate an "opaque" register-type call (register-type Foo).

For structs, struct Foo {int bar int foo} we'll generate field bindings too (register-type Foo [bar Int foo Int]).