Partial suggestion filling for path parts (#1722)

* Partial suggestion filling for path parts

This makes the ctrl+right partial suggestion filling take into account path parts, as it does in fish. To be precise, if the user has typed `python /home/l` and has been shown the suggestion `python /home/lgrobol/test.py`, hitting ctrl+right will only partial fill up to `python /home/lgrobol/` instead of  `python /home/lgrobol/test.py` (current behaviour).

src/prompt_toolkit/key_binding/bindings/auto_suggest.py

@@ -59,7 +59,7 @@ def _fill(event: E) -> None:
         suggestion = b.suggestion
 
         if suggestion:
-            t = re.split(r"(\S+\s+)", suggestion.text)
+            t = re.split(r"([^\s/]+(?:\s+|/))", suggestion.text)
             b.insert_text(next(x for x in t if x))
 
     return key_bindings