Remove NFC Slice jank

The NFC Slice would jank on enable and disable, because of the
intent filter it registered with SysUI. The intent filter would
broadcast an update for four states:
1) On
2) Off
3) Turning On
4) Turning off

The first two caused no problems. The third and fourth caused jank,
since when clicked, the switch in the NFC slice would turn on / off
asynchronously - that is, it turned on or off based on the previous
state of the switch, rather than on the actual value of NFC. It does
this to feel fluid in the app in which it is rendered.

From the off state, the order of events is:
1.  Switch clicked
2.  Switch animates on
2.  Background intent is fired to settings to turn on Nfc (happens at
       the same time as animation)
3.  Settings calls the NFC enable API
4.  A broadcast for Turning On is sent
5.  The receiver in SysUI gets the broadcast and forwards it to settings
6.  Settings tells the Slice to make sure it is up to date
7.  The Slice checks for the current value - IMPORTANTLY - which is
        currently off, it is only in the process of being enabled.
8.  The Slice flips back off
9.  Nfc finishes getting enabled in the background
10. The framework pushes the NFC ON broadcast
11. SysUI gets the broadcast, and forwards it to settings
12. Settings tells the slice to update
13. The slice checks again and finds that NFC is on, flipping on.

This CL creates a new background slice worker for NFC and registers
the intent filter there, rather than in SysUI. When the background
worker gets the broadcast, it checks if it is in state 3/4, and if so,
it drops the update silently.

Fixes: 115737701
Test: robotests
Change-Id: I17043828ad3a67a2a5acdf5c75d9cc51ff7e91d0