Note that this operation is not very intelligent -- it just
reverses the order of all Unicode code points. It may
result in non-Unicode-normalized strings and may give
strange output for bidirectional strings.
stri_reverse(c("123", "abc d e f"))
stri_reverse("ZXY (\u0105\u0104123$^).")
stri_reverse(stri_enc_nfd('\u0105')) == stri_enc_nfd('\u0105') # A, ogonek -> agonek, A