[loong64][mips64][wasm-gc][refactor] Rename optRef -> refNull

Port commit a0a78665

Bug: v8:7748
Change-Id: I23e559917a76a01a7afb78403648372149a13c54
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3743122Reviewed-by: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Auto-Submit: Liu Yu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/main@{#81510}

src/wasm/baseline/loong64/liftoff-assembler-loong64.h

@@ -852,7 +852,7 @@ void LiftoffAssembler::MoveStackValue(uint32_t dst_offset, uint32_t src_offset,
       St_w(scratch, liftoff::GetStackSlot(dst_offset));
       break;
     case kI64:
-    case kOptRef:
+    case kRefNull:
     case kRef:
     case kRtt:
     case kF64:

src/wasm/baseline/mips64/liftoff-assembler-mips64.h

@@ -955,7 +955,7 @@ void LiftoffAssembler::MoveStackValue(uint32_t dst_offset, uint32_t src_offset,
       Sw(scratch, liftoff::GetStackSlot(dst_offset));
       break;
     case kI64:
-    case kOptRef:
+    case kRefNull:
     case kRef:
     case kRtt:
     case kF64: