Detailed diff tests for block types (#2398)

This adds tests for the detailed diff output of
- List blocks
- Set blocks
- MaxItemsOne list blocks

for adding, removing, changing the property and adding, removing,
changing nested properties in the block.

A few issues here:
- #2234 affects
quite a few of the cases
- #2399 diffs
are displayed on nested properties which are not specified when a block
is removed
- #2400 diffs
are displayed on the `__defaults` property when the number of elements
in the block changes.