Return the FakeContext as application context

This avoids getApplicationContext() to return null and cause
NullPointerException.

Fixes #4392 <https://github.com/Genymobile/scrcpy/issues/4392#issuecomment-1792806080>

server/src/main/java/com/genymobile/scrcpy/FakeContext.java

@@ -2,6 +2,7 @@ package com.genymobile.scrcpy;
 
 import android.annotation.TargetApi;
 import android.content.AttributionSource;
+import android.content.Context;
 import android.content.ContextWrapper;
 import android.os.Build;
 import android.os.Process;
@@ -44,4 +45,9 @@ public final class FakeContext extends ContextWrapper {
     public int getDeviceId() {
         return 0;
     }
+
+    @Override
+    public Context getApplicationContext() {
+        return this;
+    }
 }