Account for REACT_NATIVE_DOWNLOADS_DIR inside fantom (#55148)

Summary:
Currently Fantom is completely ignoring the `REACT_NATIVE_DOWNLOADS_DIR` env variable that other scripts in the repo are instead honoring. This fixes it.

## Changelog:

[INTERNAL] -

Pull Request resolved: #55148

Test Plan: CI

Reviewed By: cipolleschi

Differential Revision: D90594286

Pulled By: cortinico

fbshipit-source-id: 872a26fc15a2acbe3c0e26035407159c20a9a285

Author: cortinico

private/react-native-fantom/build.gradle.kts

@@ -50,7 +50,12 @@ val reactNativeRootDir = projectDir.parentFile.parentFile
 val reactNativeDir = File("$reactNativeRootDir/packages/react-native")
 val reactAndroidDir = File("$reactNativeDir/ReactAndroid")
 val reactAndroidBuildDir = File("$reactAndroidDir/build")
-val reactAndroidDownloasdDir = File("$reactAndroidBuildDir/downloads")
+val reactAndroidDownloadsDir =
+    if (System.getenv("REACT_NATIVE_DOWNLOADS_DIR") != null) {
+      File(System.getenv("REACT_NATIVE_DOWNLOADS_DIR"))
+    } else {
+      File("$reactAndroidBuildDir/downloads")
+    }
 
 val testerDir = File("$projectDir/tester")
 val testerBuildDir = File("$buildDir/tester")
@@ -65,7 +70,7 @@ val createNativeDepsDirectories by
       reportsDir.mkdirs()
     }
 
-val downloadFollyDest = File(reactAndroidDownloasdDir, "folly-${FOLLY_VERSION}.tar.gz")
+val downloadFollyDest = File(reactAndroidDownloadsDir, "folly-${FOLLY_VERSION}.tar.gz")
 
 val prepareFolly by
     tasks.registering(Copy::class) {