[llvm] [VPlan] Improve code around canConstantBeExtended (NFC) (PR #161652)

[David Sherwood via llvm-commits]

https://github.com/david-arm approved this pull request.

LGTM. Before landing I think it's worth explaining in a little more detail what the "improvement" here is, either in the title or commit message. Essentially it seems like you're just changing the interface to take a APInt because this is more natural when used in combination with the match patterns.

https://github.com/llvm/llvm-project/pull/161652