Added PollingControllerOnly (#1873)

## Explanation

Added PollingControllerOnly to extend from an empty class. This will
allow classes that previously are just classes that don't extend from
BaseV2 or V2 to extend from this new PollingControllerOnly.

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### `@metamask/polling-controller`

- **ADDED**: PollingControllerOnly to extend from an empty class

---------

Co-authored-by: jiexi <[email protected]>
Co-authored-by: Alex Donesky <[email protected]>

packages/polling-controller/src/PollingController.test.ts

@@ -1,6 +1,6 @@
 import { ControllerMessenger } from '@metamask/base-controller';
 
-import { PollingController } from './PollingController';
+import { PollingController, PollingControllerOnly } from './PollingController';
 
 const TICK_TIME = 1000;
 
@@ -327,4 +327,18 @@ describe('PollingController', () => {
       ]);
     });
   });
+  describe('PollingControllerOnly', () => {
+    it('can be extended from and constructed', async () => {
+      class MyClass extends PollingControllerOnly {
+        _executePoll = createExecutePollMock();
+      }
+      const c = new MyClass();
+      expect(c._executePoll).toBeDefined();
+      expect(c.getIntervalLength).toBeDefined();
+      expect(c.setIntervalLength).toBeDefined();
+      expect(c.stopAllPolling).toBeDefined();
+      expect(c.startPollingByNetworkClientId).toBeDefined();
+      expect(c.stopPollingByPollingToken).toBeDefined();
+    });
+  });
 });

packages/polling-controller/src/PollingController.ts

@@ -183,5 +183,8 @@ function PollingControllerMixin<TBase extends Constructor>(Base: TBase) {
   return PollingControllerBase;
 }
 
+class Empty {}
+
+export const PollingControllerOnly = PollingControllerMixin(Empty);
 export const PollingController = PollingControllerMixin(BaseControllerV2);
 export const PollingControllerV1 = PollingControllerMixin(BaseController);