Android: Add ProGuard keep rules for classes and methods referenced in IDCache

Co-authored-by: OatmealDome <julian@oatmealdome.me>

Source/Android/app/proguard-rules.pro

@@ -12,3 +12,8 @@
 -dontwarn org.openjsse.javax.net.ssl.SSLParameters
 -dontwarn org.openjsse.javax.net.ssl.SSLSocket
 -dontwarn org.openjsse.net.ssl.OpenJSSE
+
+# This is referenced in JNI_OnLoad.
+-keep class androidx.core.util.Pair {
+    <init>(java.lang.Object, java.lang.Object);
+}