R1:039a5a6d8618

Simplify hunk parsing

Summary:
Simplify whitespace-ignoring diffing:

- Currently, we generate two diffs (one ignoring whitespace, one normal) and then copy the //text content// from the normal one to the whitespace-ignoring one.
- Instead, copy the //change types// from the ignoring one to the normal one.
- This is cheaper and much simpler.
- It means that we have the right change types in reparseHunksForSpecialAttributes(), and can simplify some other things.

Simplify whitespace changes…