clamp: improve error handling and error messages.

[ysiraichi]

This PR refactors the clamp operation implementation by improving its error message, and returning a status type value.

Key Changes:

• Make tensor_methods::clamp return StatusOr<XLATensorPtr>
• Improve error handling
  • Inline GetMinMaxValues() function
  • Move the check to a new CheckClampMinOrMax() function

Example

a = torch.rand(10, device=device)
torch.ops.aten.clamp.default(a)

Before:

Traceback (most recent call last):
  File "examples/clamp.py", line 6, in <module>
    torch.ops.aten.clamp.default(a)
  File "torch/_ops.py", line 841, in __call__
    return self._op(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: Check failed: min || max: At least one of 'min' or 'max' must not be None (at torch_xla/csrc/tensor_methods.cpp:183)

Exception raised from operator& at torch_xla/csrc/runtime/tf_logging.cpp:26 (most recent call first):

After:

Traceback (most recent call last):
  File "examples/clamp.py", line 6, in <module>
    torch.ops.aten.clamp.default(a)
  File "torch/_ops.py", line 840, in __call__
    return self._op(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: clamp(): expected at least one of `min` or `max` arguments to be specified.

Status Propagation Trace:
    From: CheckClampMinOrMax at torch_xla/csrc/tensor_methods.cpp:496 (error: clamp(): expected at least one of `min` or `max` arguments to be specified.)
    From: clamp at torch_xla/csrc/tensor_methods.cpp:1357
    From: clamp at torch_xla/csrc/aten_xla_type.cpp:1377

Exception raised from ThrowStatusError at torch_xla/csrc/status.cpp:128 (most recent call first):