Fix AGP 9.1 compatibility issues in Gradle plugin

- ReactPlugin.kt: Use .asFile to convert Directory to File for directories.add()
- AgpConfiguratorUtils.kt: Remove deprecated libraryVariants API, directly access manifest file

These changes address AGP 9.1 API changes where libraryVariants was removed
and Directory types need to be converted to File for source set configuration.

Author: leotm

packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/ReactPlugin.kt

@@ -234,12 +234,12 @@ class ReactPlugin : Plugin<Project> {
     if (isLibrary) {
       project.extensions.getByType(LibraryAndroidComponentsExtension::class.java).finalizeDsl { ext
         ->
-        ext.sourceSets.getByName("main").java.directories.add(generatedSrcDir.get().dir("java"))
+        ext.sourceSets.getByName("main").java.directories.add(generatedSrcDir.get().dir("java").asFile)
       }
     } else {
       project.extensions.getByType(ApplicationAndroidComponentsExtension::class.java).finalizeDsl {
           ext ->
-        ext.sourceSets.getByName("main").java.directories.add(generatedSrcDir.get().dir("java"))
+        ext.sourceSets.getByName("main").java.directories.add(generatedSrcDir.get().dir("java").asFile)
       }
     }
 

packages/gradle-plugin/react-native-gradle-plugin/src/main/kotlin/com/facebook/react/utils/AgpConfiguratorUtils.kt

@@ -116,21 +116,16 @@ internal object AgpConfiguratorUtils {
         val components = subproject.extensions
             .getByType(LibraryAndroidComponentsExtension::class.java)
 
-        components.libraryVariants.all { variant ->
-          if (components.namespace == null) {
-            val manifestFile = variant.sourceSets
-                ?.getByName("main")
-                ?.manifest
-                ?.srcFile
-
-            manifestFile
-                ?.takeIf { it.exists() }
-                ?.let { file ->
-                  getPackageNameFromManifest(file)?.let { packageName ->
-                    components.namespace = packageName
-                  }
+        if (components.namespace == null) {
+          val manifestFile = subproject.file("src/main/AndroidManifest.xml")
+
+          manifestFile
+              .takeIf { it.exists() }
+              ?.let { file ->
+                getPackageNameFromManifest(file)?.let { packageName ->
+                  components.namespace = packageName
                 }
-          }
+              }
         }
       }
     }