cxxmodules: make export trampoline script files unique

Include the name of the `EXPORT` in the filename when generating export
information for C++ modules. This allows the same directory to be used
for multiple sets of C++ module-using targets.

For `export(TARGETS)` uses, generate a name based on the hash of the
concatenation of the target names involved with the `export()` call.

Fixes: #25609

Source/cmExportTryCompileFileGenerator.h

@@ -56,7 +56,10 @@ protected:
                               cmTargetExport* te) override;
 
   std::string GetCxxModulesDirectory() const override { return {}; }
-  void GenerateCxxModuleConfigInformation(std::ostream&) const override {}
+  void GenerateCxxModuleConfigInformation(std::string const&,
+                                          std::ostream&) const override
+  {
+  }
 
 private:
   std::string FindTargets(const std::string& prop,