message: Calculate initial height properly
  Closes
diff: @@ -591,10 +591,10 @@ namespace winrt::TerminalApp::implementation
  auto tabControl = TabRowControl();
  tabControl.Measure({ SHRT_MAX, SHRT_MAX });
  - // For whatever reason, there's about 6px of unaccounted-for space
  - // in the application. I couldn't tell you where these 6px are
  + // For whatever reason, there's about 10px of unaccounted-for space
  + // in the application. I couldn't tell you where these 10px are
  // coming from, but they need to be included in this math.
  - proposedSize.Width += (tabControl.DesiredSize().Height + 6) * scale;
  + proposedSize.Height += (tabControl.DesiredSize().Height + 10) * scale;
  }
  return proposedSize;
  