Returns an array of all index positions in the array containing items.
For multi-dimensional Arrays, each returned index will be an array of index
values.
Example 5.165. Array class — allIndexes method
a=.array~of("Fred","Mike","David")donameovera~allIndexessayname-- displays "1", "2", and "3"enda~remove(2)-- remove second itemdonameovera~allIndexessayname-- displays "1" and "3"end