Add support for a new data format that differentiates between comparison and diff.

[abeaumont]

Currently, we have a single double format to handle both cases, with some optional fields to differentiate between both cases. This is not robust and causes problems as the one described in #762.

Additionally, there's some information needed for rendering that is not being included in the format (see https://github.com/pyroscope-io/pyroscope/pull/785#pullrequestreview-869283471).

We'd need a new data format to address both cases. Ideally, we could support this without a version bump in the data format, but as the format is versioned, it's also OK to bump the version if needed as long as we provide mapping functions.