add FirebaseAppCheckKtxRegistrar to appcheck-ktx (#4003)

* add FirebaseAppCheckKtxRegistrar to appcheck-ktx

* add missing imports

* remove keep annotation

Author: thatfiredev

appcheck/firebase-appcheck/ktx/src/main/kotlin/com/google/firebase/appcheck/ktx/FirebaseAppCheck.kt

@@ -14,10 +14,14 @@
 
 package com.google.firebase.appcheck.ktx
 
+import com.google.firebase.BuildConfig
 import com.google.firebase.FirebaseApp
 import com.google.firebase.appcheck.AppCheckToken
 import com.google.firebase.appcheck.FirebaseAppCheck
+import com.google.firebase.components.Component
+import com.google.firebase.components.ComponentRegistrar
 import com.google.firebase.ktx.Firebase
+import com.google.firebase.platforminfo.LibraryVersionComponent
 
 /** Returns the [FirebaseAppCheck] instance of the default [FirebaseApp]. */
 val Firebase.appCheck: FirebaseAppCheck
@@ -39,3 +43,10 @@ operator fun AppCheckToken.component1() = token
  * @return the expireTimeMillis of the [AppCheckToken]
  */
 operator fun AppCheckToken.component2() = expireTimeMillis
+
+internal const val LIBRARY_NAME: String = "fire-app-check-ktx"
+
+class FirebaseAppCheckKtxRegistrar : ComponentRegistrar {
+    override fun getComponents(): List<Component<*>> =
+            listOf(LibraryVersionComponent.create(LIBRARY_NAME, BuildConfig.VERSION_NAME))
+}