Pathlib in core.magics

[MrMino]

See #12515.

This introduces usage of pathlib, including in places where it could be used instead of os.path, in:

• IPython.core.magics.execution
• IPython.core.magics.packaging

Don't be scared by the amount of edited lines. By the boy-scout rule I've fixed some issues with code style that my linter was yapping about: redundant or missing whitespace / lines, wrong indentation, unnecessary usage of \. These changes shouldn't alter any behavior. In IPython.core.magics.execution it turned out to be a lot of hunks.

[MrMino]

Turns out I had to move the code style changes out, because darkening them is a whole other big can of worms. They now live here. Not sure if I should PR partial style changes.

Also, I decided not to add the following change, as it didn't visibly improve anything:

IPython/core/magics/execution.py:
-            args = shellglob(map(os.path.expanduser,  arg_lst[1:]))
+            args = shellglob(map(lambda p: str(Path(p).expanduser()), arg_lst[1:]))

I wonder if IPython.utils.path.shellglob still adds value, given it was implemented back in 2012.

[Carreau]

Don't worry f the code formatting is too-agressive, we can disable it.

This looks great ! Thanks !