Add emulation of word motion in Vim(e.g. w, b, e)

[pit-ray]

Add word-motion, which behaves almost exactly like the original Vim.

Outline

• Capture text containing a few words with the clipboard.
• Break grapheme cluster with ICU to synchronize cursor and string positions. In fact, you can optionally specify whether to split by code points or by grapheme cluster.
• Then, based on the code points, the punctuation character is determined using an function based on utf_class in Vim.
  (ref. https://github.com/vim/vim/blob/master/src/mbyte.c#L2787-L2903)
• Move the cursor based on the punctuation.