Add contentDescription to MediaProjection screen recording dialog

Talkback was only announcing "ON/OFF" and a text description of the switch, so adding contentDescription so now there will be a description of what the switch corresponds to.

Fix: 308372488
Test: Manual testing
Flag: None
Change-Id: I7e04697adeb137d7d92e3c5937f879ac542d39ee
1 file changed