Previously, in asan builds we attempted to use an undefined variable in instantiateWasm
so we would crash on startup. This fixes it.

I figured out a way to remove the super inefficient `calculate_wasm_func_nargs_fallback` and
replace it with wasm-gc code. This should perform much better. The cpython patch message says:

Part of the ongoing quest to support JSPI. The JSPI spec removed its dependence on
JS type reflection, and now the plan is for runtimes to ship JSPI while keeping
type reflection in stage 3. So we need an alternative way to count the number of
parameters of a function. It is possible to count them by repeatedly trying to
instantiate a webassembly module with the function as an import of a different type
signature. But this is pretty inefficient.

Since WebAssembly gc is now stage 4, there is a new option. WebAssembly gc added the
`ref.test` instruction which can ask if a funcref has a given type. It's a bit difficult
to apply because even our usual assembler the wasm binary toolkit doesn't support this
instruction yet. But all JS engines that support JSPI support it. We just have to do some
manual work to produce the binary.

This code also has to be written carefully to interact properly with memory snapshots.
Importantly, no JS initialization code can be called from the C initialization code.
For this reason, we make a C function pointer to fill from JS and fill it in a preRun
function.

Upstream PR:
python/cpython#128628