Fix BUCK build (#27826)

Summary:
This fixes a build failure with buck introduced with #27729. The internal and external buck overlays diverged in how fbjni was imported. The Buck re-export here ensures that the targets resolve both internall and externally.

## Changelog

[Android] [Fixed] - RNTester Buck Build
Pull Request resolved: #27826

Test Plan:
buck fetch rntester
buck build rntester

Reviewed By: jknoxville

Differential Revision: D19496769

Pulled By: passy

fbshipit-source-id: d699a5f64f691ed375cfc7a9d6a5a6f6e36ba283

Author: passy

ReactAndroid/src/main/libraries/fbjni/java/com/facebook/fbjni/BUCK renamed to ReactAndroid/src/main/libraries/fbjni/BUCK

@@ -1,7 +1,7 @@
 load("//tools/build_defs:fb_native_wrapper.bzl", "fb_native")
 
 fb_native.android_library(
-    name = "fbjni",
+    name = "java",
     exported_deps = [
         ":fbjni-binary",
     ],