tests: Add specific test for closures in native emitter.

tests/micropython/native_closure.py

+# test native emitter can handle closures correctly
+
+# basic closure
+@micropython.native
+def f():
+    x = 1
+    @micropython.native
+    def g():
+        nonlocal x
+        return x
+    return g
+print(f()())
+
+# closing over an argument
+@micropython.native
+def f(x):
+    @micropython.native
+    def g():
+        nonlocal x
+        return x
+    return g
+print(f(2)())
+
+# closing over an argument and a normal local
+@micropython.native
+def f(x):
+    y = 2 * x
+    @micropython.native
+    def g(z):
+        return x + y + z
+    return g
+print(f(2)(3))

tests/micropython/native_closure.py.exp

+1
+2
+9