解决Button无法居中显示字符，特别是Webdings这类图形字符

Reference： https://stackoverflow.com/questions/17469159/centering-text-on-a-button

btnUp.Text = "▲";
btnDown.Text = "▼";
btnUp.TextAlign = ContentAlignment.MiddleCenter;
btnDown.TextAlign = ContentAlignment.MiddleCenter;
btnUp.UseCompatibleTextRendering = True
btnDown.UseCompatibleTextRendering = True