[BUG] <...> lowers to unnamed pack #708

Title: <...> lowers to unnamed pack.

Description:

Since commit 025d7af, ... is an identifier.
So ... in a template-parameter-declaration-list lowers to typename ...,
just like T would lower to typename T.

Feature or bug?
I call bug.
#603 makes it so that template template parameters are emitted.
Because it chooses to lower them unnamed, it lowers T: <...> to template<typename> class T.
The existing branch in main to print a pack's ellipsis,
if (n.declaration->is_variadic) { (https://github.com/hsutter/cppfront/pull/603/files#diff-e683e1259bbc0d6de7f1fbf797fb772f31a0a1ef2254ec317d15c298102fa3f3R3931)
isn't exercised because it the declaration isn't variadic (it's name just happens to be ...).

Minimal reproducer (https://cpp2.godbolt.org/z/YbzMc3dh3):

f: <...> () = { }
main: () = { }

cppfront main.cpp2
clang++18 -std=c++23 -stdlib=libc++ -lc++abi -pedantic-errors -Wall -Wextra -Wconversion -Werror=unused-result -I . main.cpp

Expected result: A diagnostic due to naming a declaration ....

Actual result and error:

Program returned: 0

template<typename ...> auto f() -> void{}

//=== Cpp2 type declarations ====================================================


#include "cpp2util.h"



//=== Cpp2 type definitions and function declarations ===========================

template<typename ...> auto f() -> void;
auto main() -> int;


//=== Cpp2 function definitions =================================================

template<typename ...> auto f() -> void{}
auto main() -> int{}