Add the "tracking-vector" class to the security section.

This follows
https://w3c.github.io/fingerprinting-guidance/#mark-fingerprinting and makes
it clear that this API can increase the fingerprinting surface despite the
proposed mitigations.

index.bs

@@ -214,7 +214,7 @@ Examples {#examples}
 Security and Privacy Considerations {#security-and-privacy}
 ===================================
 
-Ambient Light Sensor provides information about lighting conditions near
+<p tracking-vector>Ambient Light Sensor provides information about lighting conditions near
 the device environment. Potential privacy risks include:
 
   - Profiling. Ambient Light Sensor can leak information about user's use