This is a more restrictive and opinionated set of rules based on the
AirBnB style guide that reduces the degrees of freedom and bikeshedding
across the repo, as well as generally representing Thesis best
practices.

A few notes:
- This definitively moves us from a prior expressed preference for
  conditional React rendering of condition ? <Element /> : <></> to the
  more common null-punning approach of condition && <Element />. The
  style used in the past is disallowed by react/no-jsx-useless-fragment,
  which is part of the default airbnb style and therefore inherited
  through the Thesis config.
- That rule also shifted a few places where we were returning <></> to
  return null instead, and updated return types accordingly. In one or
  two places where doing that would have a far-reaching impact, an
  eslint-ignore is used for now (with clarifying comment of course),
  which can be revisited in the future if we feel strongly about it.
- This also pushes us away from the pattern of having () => {}-style
  functions with a single return statement inside, favoring instead
  making these return implicitly. A lot of the changes are around that.
- There were also a few cases where undefineds were being left to dangle
  that got flagged and now get alternate empty states. Delightful!

Last but not least, one whole rule is disabled so that we can get the
core of this merged: react/no-unstable-nested-components has flagged a
bunch of places where another pattern adopted in the current codebase
(defining anonymous functions that return elements lazily) is being used
in a way that's creating a lot of unnecessary diffs. Probably not
impactful in the large, but regardless it would be good to fix this in
the future, for now the rule is turned off with a FIXME comment.