[Issue 16673] improve cyclic module imports checker

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16673

--- Comment #6 from Martin Nowak <code at dawg.eu> ---
Should be fairly easy with the new 2-step lookup process (SearchLocalsOnly,
SearchImportsOnly), just instrument all symbol searches in expression.d to tag
the current scope's func as usesImports, when only the SearchImportsOnly lookup
returns a symbol.
Furthermore CallExp's using such functions also need to tag their scope's
function to make it work transitively.

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