message: [vtbackend] ViCommands: Fixes `M` motion to take viewport into account.
diff: @@ -578,7 +578,8 @@ CellLocation ViCommands::translateToCellLocation(ViMotion motion, unsigned count
  -_terminal.currentScreen().historyLineCount().as<LineOffset>()),
  cursorPosition.column };
  case ViMotion::LinesCenter: // M
  - return { max(LineOffset(0), LineOffset::cast_from(_terminal.pageSize().lines / 2 - 1)),
  + return { LineOffset::cast_from(_terminal.pageSize().lines / 2 - 1)
  + - boxed_cast<LineOffset>(_terminal.viewport().scrollOffset()),
  cursorPosition.column };
  case ViMotion::PageDown:
  return { min(cursorPosition.line + LineOffset::cast_from(_terminal.pageSize().lines / 2),
  