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

首先在替换模式 (r) 下复现报告中的 macOS Option 键序列，并将其与插入模式进行比较，重点关注标记文本和输入法的处理。完成的标准是：该序列在替换一个字符时产生带重音符号的字符，同时不禁用“Draw marked text inline.”