fix(@angular/cli): ng g show descrption from collection.json if not present in schema.json

Wiht this change we show the descrption from `collection.json` if not present in schematic `schema.json` in  `ng generate` help output

Author: alan-agius4

packages/angular/cli/src/commands/generate/cli.ts

@@ -68,16 +68,21 @@ export class GenerateCommandModule
 
     for (const schematicName of schematicNames) {
       const {
-        description: { schemaJson, aliases: schematicAliases, hidden: schematicHidden },
+        description: {
+          schemaJson,
+          aliases: schematicAliases,
+          hidden: schematicHidden,
+          description: schematicDescription,
+        },
       } = collection.createSchematic(schematicName, true);
 
       if (!schemaJson) {
         continue;
       }
 
       const {
-        description,
         'x-deprecated': xDeprecated,
+        description = schematicDescription,
         aliases = schematicAliases,
         hidden = schematicHidden,
       } = schemaJson;