Add reverse to the R-Instat string functions

[rdstern]

I am suggesting @anastasia-mbithe for this, because she is already working on the calculator. Also this is a function I am assuming for the maths camps!

Could a function called reverse be added to the text/string keyboard

I suggest it could go on the second-to-bottom row so the keys line up with the bottom row, each having 6 keys.
it gives stringi::stri_reverse( ) (notice it is stringi, and not stringr, which is why I missed it before)