Fix #341 CJK Problem.

[rebornix]

Yay! We love PRs! 🎊

Please include a description of your change & check your PR against this list, thanks:

• Commit message has a short title & issue references
• Commits are squashed
• It builds and tests pass (e.g gulp tslint)

Two impoartant things to note here:

1. We are handing type events asynchronously, in which case, default:replacePreviousChar might be executed before our customized type event. When we type in CJK characters, we are typing English characters firstly then replace them with the desired CJK character/s. If the replacePreviousChar happens before its corresponding type event, we are running into chaos.
2. We are maintaining cursorPosition in vimState and we will leverage this state to implement dot repeat somehow. However, when we perform type then replacePreviousChar, it will ruin our cursorPosition maintaining. So we should always update the cusor info after triggering default:replacePreviousChar.

After this fix, the CJK typing experience in Insert Mode is likely perfect (I'm not 100% sure whether there would be other issues as I just write Chinese). CJK handling in Normal Mode is still blocked by VS Code right now but the priority is really low, why would you bother tying CJK while using Vim commands?

[johnfn]

Nice!