When a11y is enabled, device entry icon is also clickable

In addition to the device entry icon longpress, when a11y
is enabled, make the device entry icon clickable too so it's easier
for the user to interact with it when a11y features like talkback are
enabled. We don't want the icon to be clickable when a11y isn't enabled
because this can lead to false-touches entering the device.

Flag: ACONFIG com.android.systemui.device_entry_udfps_refactor NEXTFOOD
Fixes: 336313562
Test: atest DeviceEntryIconViewModelTest
Test: manually enable talkback and observe "double click" can be used
to act on the device entry icon in addition to "click and then hold"

Change-Id: I04cb421d1f2f75d51356801df9f0a71e6b655131