[mlir] Add initial graphdef->mlir generation
[mlir] Add initial graphdef->mlir generation

This CL adds:
  * One graphdef extracted from the TF test suite. More will come.
  * Scaffolding for the "graphdef2mlir" tool.
  * Importing of simple graphs. Type inference is not yet working, and attributes do not work either.
  * A fix for CFGFunction::~CFGFunction to not die if the function was destroyed without a terminator (for example if we exit early due to an error).

PiperOrigin-RevId: 206965992

DavidNorman/tensorflow,adit-chandra/tensorflow,gunan/tensorflow,Intel-Corporation/tensorflow,jhseu/tensorflow,davidzchen/tensorflow,DavidNorman/tensorflow,freedomtan/tensorflow,paolodedios/tensorflow,annarev/tensorflow,Intel-tensorflow/tensorflow,aam-at/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-pywrap_saved_model,petewarden/tensorflow,jhseu/tensorflow,annarev/tensorflow,adit-chandra/tensorflow,aldian/tensorflow,tensorflow/tensorflow,ppwwyyxx/tensorflow,petewarden/tensorflow,tensorflow/tensorflow,Intel-tensorflow/tensorflow,gunan/tensorflow,adit-chandra/tensorflow,arborh/tensorflow,DavidNorman/tensorflow,annarev/tensorflow,tensorflow/tensorflow-pywrap_saved_model,ppwwyyxx/tensorflow,sarvex/tensorflow,ppwwyyxx/tensorflow,gautam1858/tensorflow,karllessard/tensorflow,aam-at/tensorflow,tensorflow/tensorflow,renyi533/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-pywrap_saved_model,DavidNorman/tensorflow,yongtang/tensorflow,arborh/tensorflow,cxxgtxy/tensorflow,tensorflow/tensorflow,cxxgtxy/tensorflow,ppwwyyxx/tensorflow,gunan/tensorflow,gautam1858/tensorflow,aldian/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,frreiss/tensorflow-fred,freedomtan/tensorflow,gunan/tensorflow,ppwwyyxx/tensorflow,petewarden/tensorflow,gautam1858/tensorflow,xzturn/tensorflow,tensorflow/tensorflow-pywrap_saved_model,jhseu/tensorflow,DavidNorman/tensorflow,gunan/tensorflow,freedomtan/tensorflow,aldian/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,xzturn/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,davidzchen/tensorflow,gunan/tensorflow,renyi533/tensorflow,yongtang/tensorflow,aam-at/tensorflow,renyi533/tensorflow,DavidNorman/tensorflow,adit-chandra/tensorflow,Intel-Corporation/tensorflow,paolodedios/tensorflow,gautam1858/tensorflow,jhseu/tensorflow,tensorflow/tensorflow-pywrap_saved_model,Intel-tensorflow/tensorflow,aam-at/tensorflow,yongtang/tensorflow,Intel-Corporation/tensorflow,karllessard/tensorflow,paolodedios/tensorflow,freedomtan/tensorflow,xzturn/tensorflow,davidzchen/tensorflow,arborh/tensorflow,freedomtan/tensorflow,frreiss/tensorflow-fred,frreiss/tensorflow-fred,aam-at/tensorflow,petewarden/tensorflow,karllessard/tensorflow,yongtang/tensorflow,adit-chandra/tensorflow,tensorflow/tensorflow,yongtang/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-experimental_link_static_libraries_once,aam-at/tensorflow,gunan/tensorflow,freedomtan/tensorflow,yongtang/tensorflow,aldian/tensorflow,petewarden/tensorflow,xzturn/tensorflow,davidzchen/tensorflow,paolodedios/tensorflow,karllessard/tensorflow,annarev/tensorflow,frreiss/tensorflow-fred,jhseu/tensorflow,gunan/tensorflow,karllessard/tensorflow,annarev/tensorflow,adit-chandra/tensorflow,Intel-tensorflow/tensorflow,renyi533/tensorflow,cxxgtxy/tensorflow,Intel-Corporation/tensorflow,tensorflow/tensorflow,xzturn/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,adit-chandra/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,paolodedios/tensorflow,DavidNorman/tensorflow,DavidNorman/tensorflow,tensorflow/tensorflow-pywrap_saved_model,jhseu/tensorflow,ppwwyyxx/tensorflow,freedomtan/tensorflow,renyi533/tensorflow,frreiss/tensorflow-fred,petewarden/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,renyi533/tensorflow,paolodedios/tensorflow,adit-chandra/tensorflow,adit-chandra/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,DavidNorman/tensorflow,yongtang/tensorflow,arborh/tensorflow,tensorflow/tensorflow-pywrap_saved_model,xzturn/tensorflow,sarvex/tensorflow,davidzchen/tensorflow,davidzchen/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_saved_model,renyi533/tensorflow,aldian/tensorflow,Intel-Corporation/tensorflow,adit-chandra/tensorflow,gunan/tensorflow,arborh/tensorflow,karllessard/tensorflow,petewarden/tensorflow,karllessard/tensorflow,davidzchen/tensorflow,annarev/tensorflow,ppwwyyxx/tensorflow,arborh/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,davidzchen/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,gautam1858/tensorflow,yongtang/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,sarvex/tensorflow,aam-at/tensorflow,renyi533/tensorflow,cxxgtxy/tensorflow,aam-at/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_saved_model,freedomtan/tensorflow,cxxgtxy/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,arborh/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-experimental_link_static_libraries_once,DavidNorman/tensorflow,paolodedios/tensorflow,frreiss/tensorflow-fred,Intel-tensorflow/tensorflow,gautam1858/tensorflow,gautam1858/tensorflow,renyi533/tensorflow,ppwwyyxx/tensorflow,sarvex/tensorflow,arborh/tensorflow,Intel-tensorflow/tensorflow,aam-at/tensorflow,cxxgtxy/tensorflow,tensorflow/tensorfl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