bug#50459: 28.0.50; Python shell completion is incompatible with flex, orderless, etc.

[Augusto Stoffel]

If I start a Python shell on Emacs -Q and type, say

```
x = []
x.c<tab>
```

then I see, as expected,

```
Possible completions are:
x.clear
x.copy
x.count
```

Now, if I (setq completion-styles '(flex)), then no completions as
reported in the same situation.  Same thing with the `orderless' or
`substring' completion styles.

Moreover, the same observation holds for native completion on or off.