fix: allow torch.Symint in slice_scatter_decomposition

[jiwoong-choi]

fix: allow torch.Symint objects for start, end and step in slice_scatter_decomposition

Description

When an exported program is torch.exported with dynamic shapes, the start, end and step could be torch.SymInt instead of int. As a result, the assertions on start, end and step in slice_scatter_decomposition aborts the lowering pass.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• [v] My code follows the style guidelines of this project (You can use the linters)
• [v] I have performed a self-review of my own code
• [v] I have commented my code, particularly in hard-to-understand areas and hacks
• I have made corresponding changes to the documentation
• I have added tests to verify my fix or my feature
• New and existing unit tests pass locally with my changes
• [v] I have added the relevant labels to my PR in so that relevant reviewers are notified

[peri044]

I don't think our code can handle (start, end, step) to be SymInt. Can you provide a test case where you see such behavior ?

[jiwoong-choi]

I'll reopen this PR (or might open a new one with more changes) after I come with a proper test case.