Updates the alpha mask for this popup widget.

def adjustMask(self):
        """
        Updates the alpha mask for this popup widget.
        """
        if self.currentMode() == XPopupWidget.Mode.Dialog:
            self.clearMask()
            return
        
        path = self.borderPath()
        bitmap = QBitmap(self.width(), self.height())
        bitmap.fill(QColor('white'))
        
        with XPainter(bitmap) as painter:
            painter.setRenderHint(XPainter.Antialiasing)
            pen = QPen(QColor('black'))
            pen.setWidthF(0.75)
            painter.setPen(pen)
            painter.setBrush(QColor('black'))
            painter.drawPath(path)
        
        self.setMask(bitmap)