Extend zst_offset lint to detect NonNull<T> offset calculations

[Gri-ffin]

Fixes #16887

The zst_offset lint previously only checked raw pointers (*mut T / *const T) for offset calculations on zero-sized types. NonNull<T> also provides add, sub, and offset methods that are equally no-ops on ZSTs, but were not flagged.

The PR extends the lint to also check NonNull<T> receivers.

changelog: [zst_offset]: detect zero-sized NonNull<T> offset calculations.

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