fix(fullscreen magnification): Add animation to the orange border

Fade in/out when create/remove the orange fullscreen magnification
border: apply animation on the border view's alpha.

Bug: 291891390
Test: adb shell device_config put accessibility com.android.window.flags.always_draw_magnification_fullscreen_border true
      atest SystemUITests:FullscreenMagnificationControllerTest
Flag: ACONFIG always_draw_magnification_fullscreen_border DEVELOPMENT
Change-Id: I536b0f86951cff150fd8b2db5441a3c93100a28c