sequencer: define array with enum values

sequencer: define array with enum values

The todo_command_info array defines which strings match with which
todo_command enum values. The array is defined in the same order as the
enum values, but if one changed without the other, then we would have
unexpected results.

Make it easier to see changes to the enum and this array by using the
enum values as the indices of the array.

Signed-off-by: Derrick Stolee <redacted>
Signed-off-by: Junio C Hamano <redacted>