Simplify magic_py_parse

[antocuni]

Greatly simplify magic_py_parse. The ultimate goal is to be able to re-use the python parser also with this spy-specific syntax:

var x = 1
const y = 2

The old way detected var x, replaced with a single x and kept a side table with info about whether this particular NAME was by chance a var/const, and the location info.

The new approach is much simpler: the code above becomes:

var·x = 1
const·y = 2

The · is "U+00B7 MIDDLE DOT", and Python considers it a valid char for an identifier. This means that var·x is seen as a single identifier, so the python parser parses it correctly, and then the SPy parser detect this special name.

As usual, special care is needed to ensure that the source location of the rewritten file are kept the same as in the original. E.g.:

    var x: i32 = 100
    var    y     : i32 = 200

becomes:

    var·x: i32 = 100
    var····y     : i32 = 200

[antocuni]

@kanin-kearpimy this PR should make it much easier to implement spy fmt.
For reader: see also #496 (and this comment and #457 .

/cc @JeffersGlass as he reviewed #496 .