Expose ET tokenizer to clients (#6335)

Summary:
Pull Request resolved: #6335

Allow clients to access the buck target for including the tokenizer in code.

Reviewed By: tarun292

Differential Revision: D64559757

fbshipit-source-id: b235da3b59677bdbcfead1b8ce9686e6ba25c146

Author: piyengar

extension/llm/tokenizer/targets.bzl

@@ -20,6 +20,7 @@ def define_common_targets():
             "//executorch/extension/llm/export/...",
             "//bento/...",
             "//bento_kernels/...",
+            "@EXECUTORCH_CLIENTS",
         ],
         _is_external_target = True,
         deps = [