Add scope for function parameter used inside function

還沒有人認領這個 Issue。

Got send here from 'vscode-python' https://github.com/microsoft/vscode-python/issues/11594
```
def function(param1):
x = 1
return param1 * x
```
Both `x` and `param1` are variables used inside the `function`, but `param1` is a given parameter.

In the function def line `param1` has a special scope but not when used inside the function.
I'd like to have it have a special textmate scope too so I can color it and see, when I use a parameter and when a 'normal' variable.

The left side is what I want (from PyCharm) and the right side is as currently is.

該 issue 沒有列出實作檔案或測試；先找出 MagicPython 的 Python 語法醒目提示規則，並比較函式範例中的參數定義與其在函式內的使用方式。完成的標準是：參數參照取得不同於一般區域變數的 TextMate scope，且涵蓋所示範例。

由索引模型根據 Issue 內容生成。