Add support for sectioned table/collection data about tablediff HOT 3 OPEN

@ianterrell What type would we want them to give us the dataSource in? Just [[SequenceDiffable]]

from tablediff.

@kent-white no, that's not quite enough information I don't think. You could move whole sections around, and so we'll need sections to be identifiable.

from tablediff.

Update: 😢 will have to come up with a different approach then we originally thought. The approach of flattening a sectioned data source and then applying the existing algorithms to it is flawed. If you get back diff steps from the algorithm that say to move SectionA to ElementB.Index that isn't easily translated to tableview moves. Same thing goes with deleting/inserting sections. A good example for .allMoves failing is

old = [Section1, f, b, c, Section2, d, e]
new = [Section1, b, Section2, c, d, e, a]

allMoves trimmed:
move 4-2 (can't be directly translated.)
insert 6
delete 1

.lcs failing:
old - [Section1, a, Section2, b, c, d]
new - [Section1, c, Section2, d, b, a]

lcs steps
insert 4
insert 5
delete 3
insert 2
delete 2
delete 1

from tablediff.