Add slice op to Arm backend (#4072)

Summary:
Implements node visitor and tests.

Also implements a io_config in ArmQuantizer
as a fallback. The io_config
QuantizationConfig is applied to placeholders
and outputs that miss annotation after all
other annotation is applied.

The intended use is for unit testing
quantization of operations
without quantization annotators.

Change-Id: Iae7dc3f1dc2afe23776566f0e9904271cde0892a

Pull Request resolved: https://github.com/pytorch/executorch/pull/4072

Reviewed By: manuelcandales

Differential Revision: D59259968

Pulled By: digantdesai

fbshipit-source-id: 253c4e9e6fd47bfe1fb18847edc33efa2a94f5d4