gh-128627: Use __builtin_wasm_test_function_pointer_signature for Emscripten trampoline (#137470)

With https://github.com/llvm/llvm-project/pull/150201 being merged, there is 
now a better way to generate the Emscripten trampoline, instead of including 
hand-generated binary WASM content. Requires Emscripten 4.0.12.