this commit fixes following issues:
1. use `-`, `=`, `arrow key` to select candidate. which shouldn't be
handle by vim
2. use `left`, `right` to move in marked text by word. which shouldn't
be handle by vim directly
3. though inserting marked text directly into UGrid cells, bypass vim
key mapping system, only the finall insertText be inserted into vim.
so vim map like jk to esc won't affect input method.
and when input i in normal mode when input method, I can press <CR>
to confirm it and only i will send to vim.
this is also the behaviour of mac terminal.
