fix(xsnap): tolerate Symbols in console.log() arguments

The xsnap `print()` doesn't know how to print a Symbol, so until that's
fixed, here's a workaround in our `tryPrint()` function. This is the backend
of all console.log calls within the XS process.

refs Moddable-OpenSource/moddable#679

packages/xsnap/lib/console-shim.js

@@ -1,11 +1,16 @@
 /* global globalThis */
+
 function tryPrint(...args) {
   try {
     // eslint-disable-next-line
-    print(...args);
+    print(...args.map(arg => typeof arg === 'symbol' ? arg.toString() : arg));
   } catch (err) {
     // eslint-disable-next-line
     print('cannot print:', err.message);
+    args.forEach((a, i) => {
+      // eslint-disable-next-line
+      print(` ${i}:`, a.toString ? a.toString() : '<no .toString>', typeof a);
+    });
   }
 }
 

packages/xsnap/test/test-boot-lockdown.js

@@ -96,3 +96,27 @@ test('TextDecoder under xsnap handles TypedArray and subarrays', async t => {
     t.assert(pass);
   }
 });
+
+test('console - symbols', async t => {
+  // our console-shim.js handles Symbol specially
+  const bootScript = await ld.asset('../dist/bundle-ses-boot.umd.js');
+  const opts = options(io);
+  const name = 'SES lockdown worker';
+  const vat = xsnap({ ...opts, name });
+  //const vat = xsnap(opts);
+  await vat.evaluate(bootScript);
+  t.deepEqual([], opts.messages);
+  await vat.evaluate(`
+    const encoder = new TextEncoder();
+    globalThis.send = msg => issueCommand(encoder.encode(JSON.stringify(msg)).buffer);
+  `);
+  await vat.evaluate(`
+    console.log('console:', 123);
+    console.log('console:', Symbol('anonymous'));
+    console.log('console:', Symbol.for('registered'));
+    send('ok');
+  `);
+  await vat.close();
+  t.deepEqual(['"ok"'], opts.messages);
+  t.pass();
+});