fix(#MagSettingsPanel): modify content desription for buttons

For WindoeMagnificationSettings, originally the description for fullscreen button is "Switch Mode" not "FullScreen". Therefore, we modify the content description to "FullScreen". Besides, for b/271216561, the accessibility move actions should be binded to settings panel view. Originally it was binded to buttons. Therefore we modify the accessibilityDelegate and set it as the mSettingsView's accessibilityDelegate. Also, we add content description for buttons.

For MagnificationModeSwitch, since we changed to open the settings panel when tapping on the switch button, we modify the button click accessibility action description from "Switch" to "Open magnification settings".

Bug: 22092166, 271216561
Test: manually check with Talkback output
Change-Id: I39c0ddf11ce307923af3459ce3155bc7e6d6cfbb