core: Always set gc_heap_size_default to support initialize multiple …

[no1wudi]

Summary

• Updated the wasm_runtime_full_init function to always set gc_heap_size_default during initialization
• This ensures that the garbage collection heap size is correctly configured even when the runtime is initialized multiple times

Impact

• Enhances the robustness of the runtime initialization process for multi-instance environments
• No impact on single-instance use cases, but prepares the codebase for better multi-instance support in the future