--pretty-typed-clang-ast cannot print all C types

[thedataking]

Not sure anyone relies on this option, so maybe the fix here is to mark it as experimental or remove it outright. Example run on range.c from Ruby 2.6:

Pretty-printed Clang AST
typedef __int128_t = __int128

typedef __uint128_t = unsigned __int128

thread 'main' panicked at 'not yet implemented: Printer::print_type(Struct(CDeclId(7)))', c2rust-transpile/src/c_ast/print.rs:763:26
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:197
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   4: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:474
   5: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:381
   6: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:336
   7: c2rust_transpile::c_ast::print::Printer<W>::print_type
             at c2rust-transpile/src/c_ast/print.rs:763
   8: c2rust_transpile::c_ast::print::Printer<W>::print_qtype
             at c2rust-transpile/src/c_ast/print.rs:789
   9: c2rust_transpile::c_ast::print::Printer<W>::print_decl
             at c2rust-transpile/src/c_ast/print.rs:571
  10: c2rust_transpile::c_ast::print::Printer<W>::print
             at c2rust-transpile/src/c_ast/print.rs:60
  11: c2rust_transpile::transpile_single
             at c2rust-transpile/src/lib.rs:323