target_link_libraries: Fix out-of-dir linking of a list of targets

In a case like

    target_link_libraries(targetInOtherDir PUBLIC "$<1:a;b>")

then all entries in the list need to be looked up in the caller's
scope.  Previously our `::@(directory-id)` suffix would apply only
to the last entry.  Instead surround the entire entry by a pair
`::@(directory-id);...;::@` so that the `::@` syntax can encode
a directory lookup scope change evaluated as the list is processed.

Fixes: #20204

Source/cmGeneratorTarget.h

@@ -378,9 +378,14 @@ public:
     cmGeneratorTarget* Target = nullptr;
   };
   TargetOrString ResolveTargetReference(std::string const& name) const;
+  TargetOrString ResolveTargetReference(std::string const& name,
+                                        cmLocalGenerator const* lg) const;
 
   cmLinkItem ResolveLinkItem(std::string const& name,
                              cmListFileBacktrace const& bt) const;
+  cmLinkItem ResolveLinkItem(std::string const& name,
+                             cmListFileBacktrace const& bt,
+                             cmLocalGenerator const* lg) const;
 
   // Compute the set of languages compiled by the target.  This is
   // computed every time it is called because the languages can change
@@ -919,6 +924,9 @@ private:
 
   std::unordered_set<std::string> UnityBatchedSourceFiles;
 
+  bool IsLinkLookupScope(std::string const& n,
+                         cmLocalGenerator const*& lg) const;
+
   void ExpandLinkItems(std::string const& prop, std::string const& value,
                        std::string const& config,
                        const cmGeneratorTarget* headTarget,