This runs build_tools/style.fish, which runs clang-format on C++, fish_indent on fish and (new) black on python.
If anything is wrong with the formatting, we should fix the tools, but automated formatting is worth it.
This searched for package.json in any parent, so just like finding
.git and .hg directories it _needs_ to use the physical pwd because
that's what git/hg/yarn use.
In general, if you do _any_ logic on $PWD, it should be the physical
path. Logical $PWD is basically only good for display and cd-ing
around with symlinks.
[ci skip]
I had previously introduced a lot of updates and fixes to npm registry
based completions for `yarn` but hadn't ported them to `npm` as well
(although they can be dropped in as-is). This patch shares the code
between the two, which resides in an explicitly sourced multi-function
fish script.
