Additional space inserted at char 100 when a single-width emoji preceeds it

[ritchiehughes]

• Your Windows build number: (Type ver at a Windows Command Prompt)
  Microsoft Windows [Version 10.0.18362.53]
  Windows Terminal appx download from GitHub: 0.1.1211.0

• What you're doing and what's happening:

Ran a simple .NET Core 2.1 application (below) that outputs various UTF-8 emojis. Bug is that when a single-width (?) emoji is printed ("Computer Mouse"), the output includes an extra 'space' later on at character position 100. No issue when it's double-width ("Computer Disk"), :

• What's wrong / what should be happening instead:

Text following the single-width emoji should not be modified or respaced.

Code sample (using Unicode.NET package from NuGet)

using NeoSmart.Unicode;
using System;
using System.Text;

namespace DetectWindowsTerminal
{
    class Program
    {
        static void Main(string[] args)
        {
            string a  = "ABCDEFGHIJKLMNOPQRSTUVWZYZ ";
            Console.OutputEncoding = Encoding.UTF8;

            Console.WriteLine($"123456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_");
            Console.WriteLine($"--------10--------20--------30--------40--------50--------60--------70--------80--------90-------100");
            Console.WriteLine($"{a}{a}{a}[{Emoji.ComputerMouse.ToString()}]{a}{a}");
            Console.WriteLine($"{a}{a}{a}[{Emoji.ComputerDisk.ToString()}]{a}{a}");
            Console.ReadLine();
        }
    }
}

[DHowett-MSFT]

This is a couple issues. One is probably #2066 (disagreement between conpty and windows terminal about glyph width). The other is #1472 -- the Computer Mouse emoji is actually two codepoints that combine, and we, being simple and cell-based, don't understand these two codepoints to be a single grapheme cluster.