R1:de7aa2186ce2

Resolve great internal confusion about left vs right inline comments

Summary:
This code was just all kinds of wrong, but got all the common cases anyone cares
about correct.

- In edit-inline-comments.js, if isOnRight() is true, use data.right, not
data.left (derp).
- Set data.left correctly, not to the same value as data.right (derp derp).
- Set "isNewFile" based on $is_new, not $on_right (derp derp derp).

Test Plan:
- Added JS debugging code to print "OLD" vs "NEW" and "LEFT" vs "RIGHT".
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