Add some helper functions to C API.

This change adds:
  * TF_OpKernel{Context,Construction}_Failure - used by C kernels to
    report failures in their compute or construction functions

  * TF_OpKernel{Context,Construction_GetAttrType - used by C kernels to
    read TF_DataType attributes from their compute or construction
    context. A macro is used for the implementation, as there will be a
    handful of these methods in subsequent CLs and their implementation is
    boilerplate.

PiperOrigin-RevId: 229311735