Fix a list length calculation in FACT-generated adapters (#12882)

This fixes a calculation when the source memory and destination memory
have different pointer sizes. A typo meant that the destination byte
length used the source byte length by accident instead of the source
length. This isn't actually reachable at all in wasm today because
memory64 isn't available at this time for components. FACT was
originally written with memory64 support, however, to be a bit more
future-proof and the component model may be getting memory64 support
soon. For now though there's no test for this, just a minor update.

Author: alexcrichton

crates/environ/src/fact/trampoline.rs

@@ -2564,7 +2564,7 @@ impl<'a, 'b> Compiler<'a, 'b> {
         } else if src_mem_opts.ptr() == dst_mem_opts.ptr() {
             self.calculate_list_byte_len(dst_mem_opts, src_len.idx, dst_element_size)
         } else {
-            self.convert_src_len_to_dst(src_byte_len.idx, src_mem_opts.ptr(), dst_mem_opts.ptr());
+            self.convert_src_len_to_dst(src_len.idx, src_mem_opts.ptr(), dst_mem_opts.ptr());
             let tmp = self.local_set_new_tmp(dst_mem_opts.ptr());
             let ret = self.calculate_list_byte_len(dst_mem_opts, tmp.idx, dst_element_size);
             self.free_temp_local(tmp);