Add @Nullable annotation to the parameter of Object.equals() methods.

Those annotations could be inferred by some tools (like Kotlin), but the
https://checkerframework.org/ doesn't check inherited annotations
complaining about all equals() invocations that get nullable argument.

The change was generated by running

find . -name \*.java | xargs sed -i 's/public boolean equals(Object /public boolean equals(@Nullable Object /'

in the frameworks/base directory and by automatically adding and
formatting required imports if needed. No manual edits.

Bug: 170883422
Test: Annotation change only. Should have not impact.
Exempt-From-Owner-Approval: Mechanical change not specific to any component.
Change-Id: I5eedb571c9d78862115dfdc5dae1cf2a35343580

core/java/android/net/DataUsageRequest.java

@@ -16,6 +16,7 @@
 
 package android.net;
 
+import android.annotation.Nullable;
 import android.net.NetworkTemplate;
 import android.os.Parcel;
 import android.os.Parcelable;
@@ -95,7 +96,7 @@ public final class DataUsageRequest implements Parcelable {
     }
 
     @Override
-    public boolean equals(Object obj) {
+    public boolean equals(@Nullable Object obj) {
         if (obj instanceof DataUsageRequest == false) return false;
         DataUsageRequest that = (DataUsageRequest) obj;
         return that.requestId == this.requestId

core/java/android/net/IpSecTransform.java

@@ -21,6 +21,7 @@ import static com.android.internal.util.Preconditions.checkNotNull;
 
 import android.annotation.IntDef;
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.annotation.RequiresFeature;
 import android.annotation.RequiresPermission;
 import android.annotation.SystemApi;
@@ -153,7 +154,7 @@ public final class IpSecTransform implements AutoCloseable {
     /**
      * Standard equals.
      */
-    public boolean equals(Object other) {
+    public boolean equals(@Nullable Object other) {
         if (this == other) return true;
         if (!(other instanceof IpSecTransform)) return false;
         final IpSecTransform rhs = (IpSecTransform) other;

core/java/android/net/NetworkIdentity.java

@@ -20,6 +20,7 @@ import static android.net.ConnectivityManager.TYPE_WIFI;
 import static android.net.ConnectivityManager.getNetworkTypeName;
 import static android.net.ConnectivityManager.isNetworkTypeMobile;
 
+import android.annotation.Nullable;
 import android.content.Context;
 import android.net.wifi.WifiInfo;
 import android.net.wifi.WifiManager;
@@ -69,7 +70,7 @@ public class NetworkIdentity implements Comparable<NetworkIdentity> {
     }
 
     @Override
-    public boolean equals(Object obj) {
+    public boolean equals(@Nullable Object obj) {
         if (obj instanceof NetworkIdentity) {
             final NetworkIdentity ident = (NetworkIdentity) obj;
             return mType == ident.mType && mSubType == ident.mSubType && mRoaming == ident.mRoaming

core/java/android/net/NetworkStats.java

@@ -411,7 +411,7 @@ public final class NetworkStats implements Parcelable {
 
         /** @hide */
         @Override
-        public boolean equals(Object o) {
+        public boolean equals(@Nullable Object o) {
             if (o instanceof Entry) {
                 final Entry e = (Entry) o;
                 return uid == e.uid && set == e.set && tag == e.tag && metered == e.metered

core/java/android/net/NetworkTemplate.java

@@ -327,7 +327,7 @@ public class NetworkTemplate implements Parcelable {
     }
 
     @Override
-    public boolean equals(Object obj) {
+    public boolean equals(@Nullable Object obj) {
         if (obj instanceof NetworkTemplate) {
             final NetworkTemplate other = (NetworkTemplate) obj;
             return mMatchRule == other.mMatchRule