webassembly/objpyproxy: Implement JS iterator protocol for Py iterables.

This allows using JavaScript for..of on Python iterables.

Signed-off-by: Damien George <damien@micropython.org>

tests/ports/webassembly/iterator.mjs

@@ -0,0 +1,21 @@
+// Test accessing Python iterables from JavaScript via the JavaScript iterator protocol.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+mp.runPython(`
+    s = "abc"
+    l = [1, 2, 3]
+`);
+
+// Iterate a Python string.
+for (const value of mp.globals.get("s")) {
+    console.log(value);
+}
+
+// Iterate a Python list.
+for (const value of mp.globals.get("l")) {
+    console.log(value);
+}
+
+// Iterate a Python list from a built-in JavaScript constructor.
+mp.runPython("import js; print(js.Set.new([1, 2, 3]).has(3))");

tests/ports/webassembly/iterator.mjs.exp

@@ -0,0 +1,7 @@
+a
+b
+c
+1
+2
+3
+True