[browser][MT] asynch dispatch soundness #98309

make sure that functions passed to emscripten_dispatch_to_thread_async

• don't throw JS exceptions
• don't throw managed exceptions
• don't leak JS interop stack frame
• sync version propagates errors or error codes
• invoke_later_when_on_ui_thread_sync and invoke_later_when_on_ui_thread_async should catch all including "memory access out of bounds"