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previously I tightened lower_path_simple_eii for all EII paths, which also affected macro targets (eii_macro_path) and broke a number of existing EII tests. this revision restores lower_path_simple_eii to its original behavior and moves the function‑kind check into a dedicated lower_eii_decl_target used only for EII declarations, so we still reject non‑function declarations without changing the behavior of macro-based EII implementations and existing tests.

This looks marginally better than #152365 to me.
Although the right place for reporting errors like "expected definition X, found definition Y" is rustc_resolve, see e.g. PathSource::is_expected.
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r? me I'll look at this tomorrow morning but don't merge anything similar to this pr until I did

I agree with petrochenkov, this has to be solved using PathSource @enthropy7

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Moved EII declaration target validation from ast_lowering to resolve via PathSource (ExternItemImpl), so diagnostics now come from resolver

also updated tests