Improve performance of reused patterns.

Bug 1721218 has a shading pattern that was used thousands of times.
To improve performance of this PDF:
 - add a cache for patterns in the evaluator and only send the IR form once
   to the main thread (this also makes caching in canvas easier)
 - cache the created canvas radial/axial patterns
 - for shading fill radial/axial use the pattern directly instead of creating temporary
   canvas

src/display/api.js

@@ -2707,6 +2707,9 @@ class WorkerTransport {
             pageProxy.cleanupAfterRender = true;
           }
           break;
+        case "Pattern":
+          pageProxy.objs.resolve(id, imageData);
+          break;
         default:
           throw new Error(`Got unknown object type ${type}`);
       }