[tfg][graphdef_import] Fix multithreaded import shared placeholder
[tfg][graphdef_import] Fix multithreaded import shared placeholder

The placeholder value was being shared between threads, causing multithreading errors when checking for duplicate inputs. This CL moves the placeholder into the conversion state.

PiperOrigin-RevId: 445001360

gautam1858/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,yongtang/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,paolodedios/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow,karllessard/tensorflow,paolodedios/tensorflow,karllessard/tensorflow,yongtang/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,karllessard/tensorflow,yongtang/tensorflow,yongtang/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,paolodedios/tensorflow,gautam1858/tensorflow,gautam1858/tensorflow,gautam1858/tensorflow,Intel-tensorflow/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_saved_model,paolodedios/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_saved_model,karllessard/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_saved_model,Intel-tensorflow/tensorflow,yongtang/tensorflow,gautam1858/tensorflow,Intel-tensorflow/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,paolodedios/tensorflow,paolodedios/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,yongtang/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,gautam1858/tensorflow,Intel-tensorflow/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_saved_model,yongtang/tensorflow,karllessard/tensorflow,gautam1858/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow,paolodedios/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,yongtang/tensorflow,tensorflow/tensorflow-pywrap_saved_model,Intel-tensorflow/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_saved_model,yongtang/tensorflow,yongtang/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-experimental_link_static_libraries_once,paolodedios/tensorflow,yongtang/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_saved_model,gautam1858/tensorflow,gautam1858/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_tf_optimizer,karllessard/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,karllessard/tensorflow,tensorflow/tensorflow