The normal default pretty printer is not great when objects are nested
and it can get hard to read the diff.
Instead, provide a pretty printer that behaves more like when json get
indented, which allows for smaller, more meaningful differences, at
the expense of a slightly longer diff.
This does not touch the other places where the pretty printer is used,
and only updated the full diff one.
We already have the AlwaysDispatchingPrettyPrinter override of the
default pretty printer. In order to make more in depth changes, we
need to copy the upstream version in, as it doesn't lend itself well to
being extended.
This does a verbatime copy, adding provenance information at the top.
Benjamin Schubert