[Web] Enable Quota System for AI Features (#31544)

* feat: migrate from aiErrorAssist naming for disabling AI features to aiFeatures.enabled to avoid confusion

feat: keep aiErrorAssistant as setting on user object until migration is run

* feat: migrate writefull.enabled unset to instead use promotionSet false

* feat: updating to use quota based system for AI usage

* feat: hide relevant sections of quota system behind split test

* feat: ship onAiFreeTrial instead of free quota amount to project meta

* fix: renaming splitTestEnabledForUser to featureFlagEnabledForUser

* fix: v1_personal should have free trial amount of ai quota

* fix: onAiFreeTrial in projectController should account for anonymous users with no features

* feat: fixing marketing exports for ai quotas

* feat: update features epoch

* feat: move to quota tiers, and map tier to numeric allowance within rateLimiters

GitOrigin-RevId: 17763447965aae5777053b783d2601517bfe6b12

services/web/app/src/Features/SplitTests/SplitTestHandler.mjs

@@ -306,6 +306,20 @@ async function getOneTimeAssignment(splitTestName) {
   }
 }
 
+/**
+ * Checks if a feature flag is enabled for a specific user
+ *
+ * Retrieves the feature flag assignment for a user and determines if the assigned variant is 'enabled'
+ *
+ * @param {string} userId - The ID of the user to check the feature flag for
+ * @param {string} splitTestName - The unique name of the feature flag
+ * @returns {Promise<boolean>} True if the user's assigned variant is 'enabled', false otherwise
+ */
+async function featureFlagEnabledForUser(userId, splitTestName) {
+  const { variant } = await getAssignmentForUser(userId, splitTestName)
+  return variant === 'enabled'
+}
+
 /**
  * Returns an array of valid variant names for the given split test, including default
  *
@@ -802,6 +816,7 @@ export default {
   getPercentile,
   getAssignment: callbackify(getAssignment),
   getAssignmentForUser: callbackify(getAssignmentForUser),
+  featureFlagEnabledForUser: callbackify(featureFlagEnabledForUser),
   getOneTimeAssignment: callbackify(getOneTimeAssignment),
   getActiveAssignmentsForUser: callbackify(getActiveAssignmentsForUser),
   hasUserBeenAssignedToVariant: callbackify(hasUserBeenAssignedToVariant),
@@ -810,6 +825,7 @@ export default {
   promises: {
     getAssignment,
     getAssignmentForUser,
+    featureFlagEnabledForUser,
     getOneTimeAssignment,
     getActiveAssignmentsForUser,
     hasUserBeenAssignedToVariant,