tests/heapalloc_inst_call: Test for no alloc for simple object calls.

tests/micropython/heapalloc_inst_call.py

+# Test that calling clazz.__call__() with up to at least 3 arguments
+# doesn't require heap allocation.
+import micropython
+
+class Foo0:
+    def __call__(self):
+        print("__call__")
+
+class Foo1:
+    def __call__(self, a):
+        print("__call__", a)
+
+class Foo2:
+    def __call__(self, a, b):
+        print("__call__", a, b)
+
+class Foo3:
+    def __call__(self, a, b, c):
+        print("__call__", a, b, c)
+
+f0 = Foo0()
+f1 = Foo1()
+f2 = Foo2()
+f3 = Foo3()
+
+micropython.heap_lock()
+f0()
+f1(1)
+f2(1, 2)
+f3(1, 2, 3)
+micropython.heap_unlock()

tests/micropython/heapalloc_inst_call.py.exp

+__call__
+__call__ 1
+__call__ 1 2
+__call__ 1 2 3