This mostly exist for
- Knowing of the value came from the command-line but we now have
`ArgMatches::source`
- Counting the number of flags but we now have `ArgAction::Count`
We were independently starting occurrences and starting value groups.
Now we do them at the same time.
COMPATIBILITY: This changes us from counting occurrences per positional
when using `multiple_values` to one occurrence. This is user visible
and tests were written against it but it goes against the documentation
and doesn't quite make sense.
This is prep for moving the derive tests. Besides organizing the test
folder for each API, this should reduce link time at the cost of
re-compiling more when a test changes.
