Scaffolding for int8 calibration in TF-TRT (#17309)

* Scaffolding for int8 calibration

* Add ops/trt_calib_op.cc

* Rename files and replace std::string with string

* Line lengths, variable names, conditionals in BUILD

* mode variable renaming

* More fixes for review

* Run clang-format

* Fix the build failue and replace the macro with a function

* Add TODO(aaroey) for future PRs

* Fix namespace for internal build

* Fix mismatched argument name and unused includes to make internal build happy

* Fix order of dependencies in BUILD file

* Remove dangling #undef