[BUG] Native compilation has RecomputeFieldValue warnings

**Description:**
When compiling a project with fastjson2 in native mode, the build logs have the following:
```
Warning: RecomputeFieldValue.FieldOffset automatic field value transformation failed. The automatic registration was attempted because a call to sun.misc.Unsafe.objectFieldOffset(Field) was detected in the class initializer of com.alibaba.fastjson2.util.JDKUtils. Detailed failure reason(s): Could not determine the field where the value produced by the call to sun.misc.Unsafe.objectFieldOffset(Field) for the field offset computation is stored. The call is not directly followed by a field store or by a sign extend node followed directly by a field store.
Warning: RecomputeFieldValue.FieldOffset automatic field value transformation failed. The automatic registration was attempted because a call to sun.misc.Unsafe.objectFieldOffset(Field) was detected in the class initializer of com.alibaba.fastjson2.util.JDKUtils. Detailed failure reason(s): Could not determine the field where the value produced by the call to sun.misc.Unsafe.objectFieldOffset(Field) for the field offset computation is stored. The call is not directly followed by a field store or by a sign extend node followed directly by a field store.
Warning: RecomputeFieldValue.FieldOffset automatic field value transformation failed. The automatic registration was attempted because a call to sun.misc.Unsafe.objectFieldOffset(Field) was detected in the class initializer of com.alibaba.fastjson2.util.JDKUtils. Detailed failure reason(s): Could not determine the field where the value produced by the call to sun.misc.Unsafe.objectFieldOffset(Field) for the field offset computation is stored. The call is not directly followed by a field store or by a sign extend node followed directly by a field store.
Warning: RecomputeFieldValue.FieldOffset automatic field value transformation failed. The automatic registration was attempted because a call to sun.misc.Unsafe.objectFieldOffset(Field) was detected in the class initializer of com.alibaba.fastjson2.util.JDKUtils. Detailed failure reason(s): The argument of sun.misc.Unsafe.objectFieldOffset(java.lang.reflect.Field) is not a constant value or a field load that can be constant-folded., Could not determine the field where the value produced by the call to sun.misc.Unsafe.objectFieldOffset(Field) for the field offset computation is stored. The call is not directly followed by a field store or by a sign extend node followed directly by a field store.
Warning: RecomputeFieldValue.FieldOffset automatic field value transformation failed. The automatic registration was attempted because a call to sun.misc.Unsafe.objectFieldOffset(Field) was detected in the class initializer of com.alibaba.fastjson2.util.JDKUtils. Detailed failure reason(s): Could not determine the field where the value produced by the call to sun.misc.Unsafe.objectFieldOffset(Field) for the field offset computation is stored. The call is not directly followed by a field store or by a sign extend node followed directly by a field store.
Warning: RecomputeFieldValue.FieldOffset automatic field value transformation failed. The automatic registration was attempted because a call to sun.misc.Unsafe.objectFieldOffset(Field) was detected in the class initializer of com.alibaba.fastjson2.writer.ObjectWriterImplMap. Detailed failure reason(s): The argument of sun.misc.Unsafe.objectFieldOffset(java.lang.reflect.Field) is not a constant value or a field load that can be constant-folded., Could not determine the field where the value produced by the call to sun.misc.Unsafe.objectFieldOffset(Field) for the field offset computation is stored. The call is not directly followed by a field store or by a sign extend node followed directly by a field store.
Warning: RecomputeFieldValue.FieldOffset automatic field value transformation failed. The automatic registration was attempted because a call to sun.misc.Unsafe.objectFieldOffset(Field) was detected in the class initializer of com.alibaba.fastjson2.writer.ObjectWriterImplMap. Detailed failure reason(s): The argument of sun.misc.Unsafe.objectFieldOffset(java.lang.reflect.Field) is not a constant value or a field load that can be constant-folded., Could not determine the field where the value produced by the call to sun.misc.Unsafe.objectFieldOffset(Field) for the field offset computation is stored. The call is not directly followed by a field store or by a sign extend node followed directly by a field store.
```

**Environment:**
- OS: RHEL 9 (quay.io/quarkus/ubi9-quarkus-mandrel-builder-image:jdk-21)
- JDK: Openjdk-21.0.5+11
- Fastjson2 and codegen: 2.0.59
- Quarkus: 3.28.4

I don't know if it causes any problem at runtime, but apparently needs to be fixed.

Similar ticket: https://github.com/alibaba/fastjson2/issues/3108

Start by reviewing similar issue 3108 and inspecting the class initializers mentioned in com.alibaba.fastjson2.util.JDKUtils and com.alibaba.fastjson2.writer.ObjectWriterImplMap. Reproduce native compilation with the reported Quarkus, Mandrel builder, JDK, and fastjson2 versions, then check whether the warnings affect runtime. Done means the warnings are eliminated or their runtime impact is verified and documented.

Written by the indexing model from the issue text.