Modernize and document the CVS diff parser.
Review Request #10780 — Created Nov. 4, 2019 and updated
This updates the CVS diff parser to work directly on the
ParsedDiffFile, rather than the deprecated intermediary parser
dictionary. It also reduces repeated attribute accesses on the parser.
This cleans up the code a decent amount.
Along with this, the parser methods have been documented, providing
better insight into what each function is responsible for.
Unit tests pass.