commit: ignore diff whitespace settings when doing `commit -i` (issue5839)

Authored by spectral.


commit: ignore diff whitespace settings when doing commit -i (issue5839)

Previously, we respected options like diff.ignoreblanklines and
diff.ignorews. This can cause problems when the user is attempting to
actually commit the blank line change. Specifically, the split extension can get
into an infinite loop because it detects that the working copy is not clean, but
when we get the diff we don't see the changes, so it just skips popping up the
chunk selection flow, saying there's no changes to record.

These options are primarily meant for viewing diffs; it is highly unlikely that
someone is actually intending to add extraneous whitespace and have it ignored
if they attempt to interactively commit (but *not* ignored if they
non-interactively commit).

Differential Revision: