Refactor USB permission and confirm dialogs.

Avoid null description in dialog by falling back to
UsbDevice#getDeviceName() and UsbAccessory#getManufacturer()
and UsbAccessory#getModel(). Use config_usbConfirmActivity
value instead of UsbConfirmActivity.class in UsbResolverActivity.

Bug: 196780010
Test: Flashed pixel device with custom build containing the change
Test: Open camera app that requests access to USB camera. Verify that TvUsbPermissionActivity is shown and verify functionality.
Test: Have an app installed which registers for USB_DEVICE_ATTACHED broadcast in its AndroidManifest. Attach USB camera device and verify that TvUsbConfirmActivity is shown and verify functionality.
Test: atest UsbPermissionActivityTest
Change-Id: I89c4176ccd5852f5b11955d65cbf05caf5260946