refactor(core): mark effect as developer preview again (angular#52490)

Re-add the `@developerPreview` flags to `effect()`. While we don't expect
the `effect` API itself to change, we may change how other FW APIs interact
with `effect`s. Also, add a missing export for one of those effect APIs.

PR Close angular#52490

aio/content/guide/signals.md

@@ -106,6 +106,8 @@ Effects always run **at least once.** When an effect runs, it tracks any signal
 
 Effects always execute **asynchronously**, during the change detection process.
 
+Note: the `effect()` API is still in [developer preview](/guide/releases#developer-preview) as we work to integrate signal-based reactivity into the core framework.
+
 ### Use cases for effects
 
 Effects are rarely needed in most application code, but may be useful in specific circumstances. Here are some examples of situations where an `effect` might be a good solution:

goldens/public-api/core/index.md

@@ -553,6 +553,9 @@ export function effect(effectFn: (onCleanup: EffectCleanupRegisterFn) => void, o
 // @public
 export type EffectCleanupFn = () => void;
 
+// @public
+export type EffectCleanupRegisterFn = (cleanupFn: EffectCleanupFn) => void;
+
 // @public
 export interface EffectRef {
     destroy(): void;

packages/core/src/core_reactivity_export_internal.ts

@@ -29,6 +29,7 @@ export {
   effect,
   EffectRef,
   EffectCleanupFn,
+  EffectCleanupRegisterFn,
   EffectScheduler as ɵEffectScheduler,
   ZoneAwareQueueingScheduler as ɵZoneAwareQueueingScheduler,
   FlushableEffectRunner as ɵFlushableEffectRunner,

packages/core/src/render3/reactivity/effect.ts

@@ -26,11 +26,15 @@ import {assertNotInReactiveContext} from './asserts';
  * An effect can, optionally, register a cleanup function. If registered, the cleanup is executed
  * before the next effect run. The cleanup function makes it possible to "cancel" any work that the
  * previous effect run might have started.
+ *
+ * @developerPreview
  */
 export type EffectCleanupFn = () => void;
 
 /**
  * A callback passed to the effect function that makes it possible to register cleanup logic.
+ *
+ * @developerPreview
  */
 export type EffectCleanupRegisterFn = (cleanupFn: EffectCleanupFn) => void;
 
@@ -212,6 +216,8 @@ class EffectHandle implements EffectRef, SchedulableEffect {
 
 /**
  * A global reactive effect, which can be manually destroyed.
+ *
+ * @developerPreview
  */
 export interface EffectRef {
   /**
@@ -222,6 +228,8 @@ export interface EffectRef {
 
 /**
  * Options passed to the `effect` function.
+ *
+ * @developerPreview
  */
 export interface CreateEffectOptions {
   /**
@@ -251,6 +259,8 @@ export interface CreateEffectOptions {
 
 /**
  * Create a global `Effect` for the given reactive function.
+ *
+ * @developerPreview
  */
 export function effect(
     effectFn: (onCleanup: EffectCleanupRegisterFn) => void,