Add scope for function parameter used inside function

Nobody has claimed this yet.

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.

The issue names no implementation files or tests; start by locating MagicPython’s Python syntax-highlighting rules and comparing the function example’s parameter definition with its use inside the function. Done means parameter references receive a distinct TextMate scope from ordinary local variables, with coverage for the shown example.

Written by the indexing model from the issue text.