This change follows the same spirit as I2fa1b7bbb but focuses on the
file path.
Likewise, the follow-up change If8ed1e511 introduces an alternate
behavior to GitPositionTransformer for conflicts due to file deletions.
Positions without a file are mapped to patchset-level comments. The
chosen implementation allows to easily choose a different comment
location for such positions in the future if we decide that
patchset-level comments are not the best fit.
Change-Id: Idd4fbe96138a9b0829a9dd53029559685535b023
5a5dbfdf3b