Handle references to fields with inheritance in closures.

test/inheritance/inherited_fields_in_closure.wren

@@ -0,0 +1,36 @@
+class Foo {
+  new { _field = "Foo field" }
+
+  closeOverFooGet {
+    return fn { return fn { return _field } }
+  }
+
+  closeOverFooSet {
+    return fn { return fn { _field = "new foo value" } }
+  }
+}
+
+class Bar is Foo {
+  new {
+    super
+    _field = "Bar field"
+  }
+
+  closeOverBarGet {
+    return fn { return fn { return _field } }
+  }
+
+  closeOverBarSet {
+    return fn { return fn { _field = "new bar value" } }
+  }
+}
+
+var bar = new Bar
+IO.print(bar.closeOverFooGet.call.call) // expect: Foo field
+IO.print(bar.closeOverBarGet.call.call) // expect: Bar field
+bar.closeOverFooSet.call.call
+IO.print(bar.closeOverFooGet.call.call) // expect: new foo value
+IO.print(bar.closeOverBarGet.call.call) // expect: Bar field
+bar.closeOverBarSet.call.call
+IO.print(bar.closeOverFooGet.call.call) // expect: new foo value
+IO.print(bar.closeOverBarGet.call.call) // expect: new bar value