Remove str() calls in call/shell functions using destructuring syntax

[joerick]

While working on #386 I came across a way to remove those str() calls when combining Path and str objects. The trick is to use array destructuring syntax, e.g. ['pip', 'wheel', path_object, *flags], rather than +. This way the typechecker assumes you intended to mix the types and gives you the type List[Union[str, PathLike]].

[YannickJadoul]

Uuuuh, alright, that looks nice! Great discovery :-)
Just noting: if we need to use it multiple times, adding a statement like CallArgs = Sequence[Union[str, PathLike]] should work to create a shorter alias (not sure if it's worth it in this case, though).

Two minor style things:

• I had tried to keep the typing imports separate from the other imports, since they do not really import any functionality (and I'm still slightly annoyed we have to import those ;-) ).
• The exploded call(['pip', 'wheel', ...]) lines are spread over many lines. Is there any way to make this more compact? E.g., have something like

call(['pip', 'wheel',
        options.package_dir.resolve(),
        '-w', built_wheel_dir,
        '--no-deps',
        *get_build_verbosity_extra_flags(options.build_verbosity)
       ], env=env)

or so? But maybe I like long lines of code too much :-D

[joerick]

• I had tried to keep the typing imports separate from the other imports, since they do not really import any functionality (and I'm still slightly annoyed we have to import those ;-) ).

These changes were by VScode's 'sort imports' command. I'd guess isort would do something similar. Happy to change it back if you like? But I think we just embrace it - Python types are kinda weird, but we're in for the ride! :) also, from os import PathLike - this is just a type - should that be separate? gets kinda fuzzy.

• The exploded call(['pip', 'wheel', ...]) lines are spread over many lines. Is there any way to make this more compact? E.g., have something like

In retrospect, I agree. I've reduced it down.

[YannickJadoul]

These changes were by VScode's 'sort imports' command. I'd guess isort would do something similar. Happy to change it back if you like? But I think we just embrace it - Python types are kinda weird, but we're in for the ride! :) also, from os import PathLike - this is just a type - should that be separate? gets kinda fuzzy.

Yeah, I don't really mind. Just noticed. And since no one made remarks when I added them like that, I had assumed it was appreciated. But if it goes against code formatters, I don't feel that strongly ;-)