refactor: Split IBootstrapService to a new file and update comments

Author: jinliu9508

OneSignalSDK/onesignal/core/src/main/java/com/onesignal/core/internal/startup/IBootstrapService.kt

@@ -0,0 +1,31 @@
+package com.onesignal.core.internal.startup
+
+import com.onesignal.OneSignal
+import com.onesignal.core.internal.application.IApplicationService
+import com.onesignal.core.internal.config.ConfigModel
+import com.onesignal.core.internal.config.ConfigModelStore
+
+/**
+ * Implement and provide this interface as part of service registration to indicate the service
+ * wants to be instantiated and its [bootstrap] function called during the initialization process.
+ *
+ * When [IBootstrapService.bootstrap] is called, only [OneSignal.setAppId] have been called during
+ * [OneSignal.initWithContext].
+ *
+ * This means the following is true:
+ *
+ *  1) An appContext is available in [IApplicationService.appContext].
+ *  2) An appId is available in [ConfigModel.appId] via [ConfigModelStore.get]
+ *  3) None of the [IStartableService.start] is called
+ *
+ * When bootstrap there is no guarantee that any other data is available. Typically a bootstrap service
+ * must be instantiated immediately and will add their appropriate hooks to then respond to changes
+ * in the system.
+ */
+interface IBootstrapService {
+    /**
+     * Called when the service is to be bootstrap.  The appId and appContext have already been established.
+     */
+
+    fun bootstrap()
+}

OneSignalSDK/onesignal/core/src/main/java/com/onesignal/core/internal/startup/IStartableService.kt

@@ -15,9 +15,8 @@ import com.onesignal.core.internal.config.ConfigModelStore
  *  1) An appContext is available in [IApplicationService.appContext].
  *  2) An appId is available in [ConfigModel.appId] via [ConfigModelStore.get]
  *
- * When started there is no guarantee that any other data is available.  Typically a startable service
- * must be instantiated immediately and will add their appropriate hooks to then respond to changes
- * in the system.
+ * When started there is no guarantee that any other data is available. Typically a startable service
+ * can asynchronously start some lengthy process that doesn't require immediate use.
  */
 interface IStartableService {
     /**
@@ -26,11 +25,3 @@ interface IStartableService {
      */
     fun start()
 }
-
-internal interface IBootstrapService {
-    /**
-     * Called when the service is to be started.  The appId and appContext have already been
-     * established.
-     */
-    fun bootstrap()
-}