Auto merge of #35116 - jseyfried:groundwork_for_new_import_semantics, r=nrc

resolve: diagnostics improvement and groundwork for RFC 1560

Fixes #35115, fixes #35135, and lays groundwork for #32213 (cc #35120).
r? @nrc

diff --cc src/librustc_resolve/lib.rs
Simple merge

diff --cc src/librustc_trans/debuginfo/mod.rs
Simple merge