re-add dynamic feature flags for isInputPending (facebook#27919)

## Summary

these were removed in facebook#26617. adds
them back so we can conduct another experiment.

## How did you test this change?
`yarn test-www`

Author: noahlemen

packages/scheduler/src/forks/SchedulerFeatureFlags.www-dynamic.js

@@ -13,6 +13,12 @@
 
 export const enableProfiling = __VARIANT__;
 
+export const enableIsInputPending = __VARIANT__;
+export const enableIsInputPendingContinuous = __VARIANT__;
+export const frameYieldMs = 5;
+export const continuousYieldMs = 10;
+export const maxYieldMs = 10;
+
 export const userBlockingPriorityTimeout = 250;
 export const normalPriorityTimeout = 5000;
 export const lowPriorityTimeout = 10000;

packages/scheduler/src/forks/SchedulerFeatureFlags.www.js

@@ -16,12 +16,12 @@ export const {
   userBlockingPriorityTimeout,
   normalPriorityTimeout,
   lowPriorityTimeout,
+  enableIsInputPending,
+  enableIsInputPendingContinuous,
+  frameYieldMs,
+  continuousYieldMs,
+  maxYieldMs,
 } = dynamicFeatureFlags;
 export const enableSchedulerDebugging = true;
 export const enableProfiling: boolean =
   __PROFILE__ && enableProfilingFeatureFlag;
-export const enableIsInputPending = true;
-export const enableIsInputPendingContinuous = true;
-export const frameYieldMs = 5;
-export const continuousYieldMs = 10;
-export const maxYieldMs = 10;