New check: Ban while-loops

[nickdrozd]

The while operator is needed to make Python Turing-complete. But
unless you are implementing something like a theorem prover or an
interpreter, there is very little call to use a true while loop. In
practically every case a while loop can be converted to a for loop
with improved clarity. Seriously, how many web apps have a need for
unbounded computation?

One exception to this is the use of while loops at the tippity-top
of applications as a main execution loop. But other than that, genuine
need for while is rare.

I would like to see a check that simply flags any use of while. This
is an opinionated check, so make it an extension.

[Pierre-Sassoulas]

Yeap, definitely something that would need to be deactivated by default :)