Peel tag and restore flags off settings rows

A dumpsys settings row can end in `tag:` and, on some vendor builds, in
`isValuePreservedInRestore:` or a bare `notPreservedInRestore` token.
The parser only peeled `default:` and `defaultSystemSet:` off the end
of a record, so on a row without a default those tokens stayed inside
the value, and on a row with one they landed in `defaultSystemSet`. A
value of `0 tag:null` is not the safe value `0`, so a setting at its
safe value was reported as dangerous; these are the false positives
measured in #912.

The metadata keys are ordered fields like the rest of the record, so
`_split_fields` reads them now, which also replaces the separate
handling of the default. The bare token has no `key:` shape and is
printed last, so it is stripped first and recorded as
`isValuePreservedInRestore: false`.

The bugreport fixture gains the three row shapes from #912: a restore
flag after `defaultSystemSet:`, and a `tag:` or a bare token directly
after the value. Two of them sit on dangerous settings at their safe
value, so the unchanged alert count of one is the false-positive check.

tests/android_bugreport/test_bugreport.py

@@ -96,7 +96,7 @@ class TestBugreportAnalysis:
 
     def test_settings_module(self):
         m = self.launch_bug_report_module(Settings)
-        assert len(m.results) == 11
+        assert len(m.results) == 12
 
         assert len(m.alertstore.alerts) == 1
         assert "accessibility_enabled = 1" in m.alertstore.alerts[0].message