Preserve naming for inputs/outputs with observer insertion (#18713)

Preserve naming for inputs/outputs with observer insertion (#18713)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18713

  - Quantizer observer node output is hooked up to following node
which mutates the naming for input/output. This is not desired and
required because observer op can be a sync node

  - Quantizer is aimed for quantizing tensors so we should insert observer
op for Values that are type tensor

Reviewed By: zafartahirov

Differential Revision: D14715916

fbshipit-source-id: feca04c65a43103b46084d3548998498b19ee599