Refactor Swift FFI type handling

[bendk]

The type_ffi filter on swift is a bit confusing and should be refactored. It currently outputs the type that we want to use in the header file (e.g. int32_t). This is different than all the other bindings, which outputs the type that lower() returns (Int32 in this case).

┆Issue is synchronized with this Jira Task ┆friendlyId: UNIFFI-113

[jhugman]

I wonder if this should prompt us to break the file in to a gen_swift and gen_header files, with two different filters modules?

use  super::header_filters as filters;

[bendk]

This was fixed by #1106.