Process: Make WIFI_UID a public API constant

The Process.WIFI_UID constant is referenced by the wifi mainline module & hence
needs to be a formal API constant. There are some other
subsystem uid's like PHONE_UID which are already public constants, so
there is precedence for making these uid's public if necessary?

Bug: 147396785
Test: Compiles
Change-Id: I85008965f9017e208c501c5a349f7e60cc102e0f

api/current.txt

@@ -35827,6 +35827,7 @@ package android.os {
     field public static final int THREAD_PRIORITY_URGENT_AUDIO = -19; // 0xffffffed
     field public static final int THREAD_PRIORITY_URGENT_DISPLAY = -8; // 0xfffffff8
     field public static final int THREAD_PRIORITY_VIDEO = -10; // 0xfffffff6
+    field public static final int WIFI_UID = 1010; // 0x3f2
   }
 
   public abstract class ProxyFileDescriptorCallback {

core/java/android/os/Process.java

@@ -68,10 +68,9 @@ public class Process {
     public static final int LOG_UID = 1007;
 
     /**
-     * Defines the UID/GID for the WIFI supplicant process.
-     * @hide
+     * Defines the UID/GID for the WIFI native processes like wificond, supplicant, hostapd,
+     * vendor HAL, etc.
      */
-    @UnsupportedAppUsage
     public static final int WIFI_UID = 1010;
 
     /**