Do not build Swift interface files into binary modules when performing a canImport query.

We should hold off actually building the binary module file until it is imported.
`canImport` queries can happen, for example, during dependency scanning, when we do not wish to have the scanner tool execute any module builds.

Resolves rdar://82603098

unittests/FrontendTool/ModuleLoadingTests.cpp

@@ -128,7 +128,8 @@ protected:
       loader->findModuleFilesInDirectory({moduleName, SourceLoc()},
         SerializedModuleBaseName(tempDir, SerializedModuleBaseName("Library")),
         /*ModuleInterfacePath*/nullptr,
-        &moduleBuffer, &moduleDocBuffer, &moduleSourceInfoBuffer, /*IsFramework*/false);
+        &moduleBuffer, &moduleDocBuffer, &moduleSourceInfoBuffer,
+        /*skipBuildingInterface*/ false, /*IsFramework*/false);
     ASSERT_FALSE(error);
     ASSERT_FALSE(diags.hadAnyError());