[flang] Catch untyped entities in interfaces with IMPLICIT NONE (#109018)

The order of operations in name resolution wasn't converting named
entities to objects by the time that they were subjected to the implicit
typing rules in the case of interface blocks. This led to entities
remaining untyped without error, leading to a crash in module file
generation.

Fixes #108975.

Author: klausler

flang/lib/Semantics/resolve-names.cpp

@@ -8748,6 +8748,9 @@ void ResolveNamesVisitor::FinishSpecificationPart(
   CheckImports();
   for (auto &pair : currScope()) {
     auto &symbol{*pair.second};
+    if (inInterfaceBlock()) {
+      ConvertToObjectEntity(symbol);
+    }
     if (NeedsExplicitType(symbol)) {
       ApplyImplicitRules(symbol);
     }

flang/test/Semantics/implicit16.f90

@@ -0,0 +1,12 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+interface
+!ERROR: No explicit type declared for 'a'
+  subroutine s(a)
+    implicit none
+  end
+!ERROR: No explicit type declared for 'f'
+  function f()
+    implicit none
+  end
+end interface
+end