Make cert selection prompt respect dark mode

Use the DayNight theme in the KeyChain certificate selection prompt such
that it is displayed using a dark theme when dark mode is set.

Test: Manual, install TestDPC, set it as Device Owner, generate keys,
and observe that the prompt shown when choosing "Test signing/validation
with a key" respects dark mode.
Bug: 152854648

Change-Id: Ifef07bb5c2c8762ebe122d35883e1df4d059467b
2 files changed