Normal mode 'r' key doesn't work with macron / IM input

In macOS, you can enter macron input using an Option key sequence. E.g. Typing <M-e>, then i should result in "í" being inputted. This works in insert mode, but if you do this in the replace mode (r command in normal mode) it doesn't work. The above key sequence will enter ´, while the i will be ignored.

This can be worked around by disabling "Draw marked text inline" in advanced preferences but is not ideal, and there may be issues with how the replace mode interfaces with other input methods (IM) as well, so investigate and fix that.

Original discussion: https://groups.google.com/forum/#!topic/vim_mac/9JuxOuUFqgg

Inizia riproducendo la sequenza del tasto Option di macOS segnalata in modalità sostituzione (r) e confrontala con la modalità inserimento, concentrandoti sulla gestione del testo contrassegnato e del metodo di input. Il lavoro è completato quando la sequenza produce il carattere accentato mentre sostituisce un carattere, senza disabilitare “Draw marked text inline.”