Update node, 15.14.0 -> 16.20.0 (#1232)

This allows us to use the native ARM64 version on MacOS.
Also update the test scripts to work on ARM64 mac, and skip tests that aren't relevant.

scripts/update_node.py

@@ -16,14 +16,15 @@ import subprocess
 import os
 import shutil
 
-version = '15.14.0'
-base = 'https://nodejs.org/dist/latest-v15.x/'
+version = '16.20.0'
+base = 'https://nodejs.org/dist/latest-v16.x/'
 upload_base = 'gs://webassembly/emscripten-releases-builds/deps/'
 
 suffixes = [
     '-win-x86.zip',
     '-win-x64.zip',
     '-darwin-x64.tar.gz',
+    '-darwin-arm64.tar.gz',
     '-linux-x64.tar.xz',
     '-linux-arm64.tar.xz',
     '-linux-armv7l.tar.xz',