Fix TensorScatter CPU security issue

[nenad1002]

Description

Fix TensorScatter CPU security issue

Motivation and Context

[Copilot]

Pull request overview

This PR addresses a CPU-side safety/security issue in the ONNX TensorScatter operator by restricting kernel registration to fixed-size tensor element types, preventing unsafe raw-buffer operations on non-fixed-size types (e.g., string). It also adds a unit test to validate that string-typed graphs are rejected during kernel resolution.

Changes:

• Restrict the CPU TensorScatter kernel type constraint from AllTensorTypes() to AllFixedSizeTensorTypes().
• Add a CPU-only unit test covering string inputs and expecting graph resolution to fail.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
onnxruntime/core/providers/cpu/llm/tensorscatter.cc	Tightens the CPU kernel type constraint to fixed-size tensor element types to avoid unsafe raw-memory operations on strings.
onnxruntime/test/providers/cpu/llm/tensorscatter_op_test.cc	Adds a regression test that attempts to bind tensor(string) to TensorScatter and expects kernel resolution to fail.