Expose AppCtxInitializer and update its doc

modules/appctx/build.gradle.kts

@@ -20,6 +20,7 @@ kotlin {
         androidMain.dependencies {
             api(AndroidX.annotation)
             implementation(AndroidX.startup.runtime)
+            implementation(splitties("experimental"))
         }
     }
 }

modules/appctx/src/androidMain/kotlin/splitties/init/AppCtxInitializer.kt

@@ -5,23 +5,38 @@
 package splitties.init
 
 import android.app.Application
+import android.content.ContentProvider
 import android.content.Context
+import androidx.startup.InitializationProvider
 import androidx.annotation.Keep
 import androidx.startup.Initializer
+import splitties.experimental.ExperimentalSplittiesApi
 
 /**
  * Initializes [appCtx] so it can be used where any [Context] can be used.
  *
- * If you use [appCtx] in another process than the default one. This will not be invoked.
- * The library will attempt to initialize [appCtx] using reflection instead. If you want to avoid
- * this, you can declare a subclass of this class in your manifest with the name of the process
- * properly specified to get it Automatically initialized. Alternatively, you can in your properly
- * declared custom [Application] call [injectAsAppCtx] passing `this` reference from the constructor
- * or the [Application.onCreate] method.
+ * If you use [appCtx] in an AndroidX App Startup [Initializer], directly or not,
+ * make sure to add this class among its list of [dependencies].
+ *
+ * If you use [appCtx] in another process than the default one this will not be invoked.
+ *
+ * If you use [appCtx] in a [ContentProvider] that is initialized before
+ * the one from AndroidX App Startup ([androidx.startup.InitializationProvider][InitializationProvider]),
+ * this will not be invoked in time.
+ *
+ * The easiest way to fix that is, in your properly declared custom [Application], to call [injectAsAppCtx],
+ * passing `this` reference from the constructor or the [Application.onCreate] method.
+ *
+ * In the case of a [ContentProvider], calling [injectAsAppCtx] in its [ContentProvider.onCreate] function
+ * will also work, but we strongly recommend you to use
+ * [AndroidX App Startup instead](https://developer.android.com/topic/libraries/app-startup),
+ * for performance reasons since each [ContentProvider] delays app startup, and these add-up,
+ * resulting in a poor UX.
  */
 @Keep // Needed because there's no default R8/proguard rules for App Startup Initializers.
 @Suppress("unused") // False positive. Used in the manifest, but tooling analysis is incomplete.
-internal class AppCtxInitializer : Initializer<AppCtxInitializer> {
+@ExperimentalSplittiesApi
+class AppCtxInitializer : Initializer<AppCtxInitializer> {
     override fun create(context: Context): AppCtxInitializer {
         context.injectAsAppCtx()
         return this