Make sure that infering params is possible from the API

jedi/inference/__init__.py

@@ -169,6 +169,8 @@ class InferenceState(object):
                 return imports.infer_import(context, name)
             if type_ == 'with_stmt':
                 return tree_name_to_values(self, context, name)
+            elif type_ == 'param':
+                return context.py__getattribute__(name.value, position=name.end_pos)
         else:
             result = follow_error_node_imports_if_possible(context, name)
             if result is not None:

test/completion/basic.py

@@ -299,6 +299,25 @@ except MyException as e:
     for x in e.my_attr:
         pass
 
+# -----------------
+# params
+# -----------------
+
+my_param = 1
+#? 9 str()
+def foo1(my_param):
+    my_param = 3.0
+foo1("")
+
+my_type = float()
+#? 20 float()
+def foo2(my_param: my_type):
+    pass
+foo2("")
+#? 20 int()
+def foo3(my_param=my_param):
+    pass
+foo3("")
 
 # -----------------
 # continuations