Fix spine can not be paused while working at realTime mode

[bofeng-song]

Re: #
#16661
cocos/cocos-engine-external#450

Changelog

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Continuous Integration

This pull request:

• needs automatic test cases check.

  Manual trigger with @cocos-robot run test cases afterward.

• does not change any runtime related code or build configuration

  If any reviewer thinks the CI checks are needed, please uncheck this option, then close and reopen the issue.

---

Compatibility Check

This pull request:

• changes public API, and have ensured backward compatibility with deprecated features.
• affects platform compatibility, e.g. system version, browser version, platform sdk version, platform toolchain, language version, hardware compatibility etc.
• affects file structure of the build package or build configuration which requires user project upgrade.
• introduces breaking changes, please list all changes, affected features and the scope of violation.

[dumganhar]

Why delete SpineSkeletonSystem ?

[bofeng-song]

Its no need an additional helper class to release the spineSkeletonInstance object.

[github-actions]

Interface Check Report

! WARNING this pull request has changed these public interfaces:

@@ -52001,8 +52001,9 @@
                 isCache: boolean;
                 isDelete: boolean;
                 enable: boolean;
                 setTrackEntryListener: any;
+                destroy();
                 initSkeleton(data: SkeletonData);
                 getAnimationState();
                 setAnimation(trackIndex: number, name: string, loop: boolean): spine.TrackEntry | null;
                 setSkin(name: string);
@@ -52204,9 +52205,9 @@
             protected _debugSlots: boolean;
             protected _enableBatch: boolean;
             protected _runtimeData: spine.SkeletonData | null;
             _skeleton: spine.Skeleton;
-            protected _instance: spine.SkeletonInstance;
+            protected _instance: spine.SkeletonInstance | null;
             protected _state: spine.AnimationState;
             protected _textures: Texture2D[];
             protected _animationName: string;
             protected _skinName: string;
@@ -67448,9 +67449,9 @@
             model: _cocos_spine_skeleton_cache__SpineModel;
             boneInfos: _cocos_spine_skeleton_cache__FrameBoneInfo[];
         }
         export class _cocos_spine_skeleton_cache__AnimationCache {
-            protected _instance: sp.spine.SkeletonInstance;
+            protected _instance: sp.spine.SkeletonInstance | null;
             protected _state: sp.spine.AnimationState;
             protected _skeletonData: sp.spine.SkeletonData;
             protected _skeleton: sp.spine.Skeleton;
             _privateMode: boolean;