Make is_package a function and call it consistently

jedi/inference/context.py

@@ -302,7 +302,6 @@ class ModuleContext(TreeContextMixin, ValueContext):
     def py__package__(self):
         return self._value.py__package__
 
-    @property
     def is_package(self):
         return self._value.is_package
 
@@ -392,6 +391,13 @@ class CompiledModuleContext(CompiledContext):
     def py__file__(self):
         return self._value.py__file__()
 
+    @property
+    def py__package__(self):
+        return self._value.py__package__
+
+    def is_package(self):
+        return self._value.is_package()
+
 
 def _get_global_filters_for_name(context, name_or_none, position):
     # For functions and classes the defaults don't belong to the