Converts git diff --word-diff=porcelain output to a Diff object.

SignificantChange Allows a structured diff to be passed into the `isSignificant` function to determine significance.

ContentChange is a part of the line that starts with ` `, `-`, `+` Consecutive ContentChange build a line.

FileDiff Source of truth: https://github.com/git/git/blob/master/diffcore.h#L106 Implemented in https://github.com/git/git/blob/master/diff.c#L3496.

Hunk is a line that starts with @@.