v8_类继承结构

Most object types in the V8 JavaScript are described in this file.
Inheritance hierarchy:
- Object
  - Smi          (immediate small integer)
  - TaggedIndex  (properly sign-extended immediate small integer)
  - HeapObject   (superclass for everything allocated in the heap)
    - JSReceiver  (suitable for property access)
      - JSObject
        - JSArray
        - JSArrayBuffer
        - JSArrayBufferView
          - JSTypedArray
          - JSDataView
        - JSCollection
          - JSSet
          - JSMap
        - JSCustomElementsObject (may have elements despite empty FixedArray)
          - JSSpecialObject (requires custom property lookup handling)
            - JSGlobalObject
            - JSGlobalProxy
            - JSModuleNamespace
          - JSPrimitiveWrapper
        - JSDate
        - JSFunctionOrBoundFunction
          - JSBoundFunction
          - JSFunction
        - JSGeneratorObject
        - JSMapIterator
        - JSMessageObject
        - JSRegExp
        - JSSetIterator
        - JSStringIterator
        - JSTemporalCalendar
        - JSTemporalDuration
        - JSTemporalInstant
        - JSTemporalPlainDate
        - JSTemporalPlainDateTime
        - JSTemporalPlainMonthDay
        - JSTemporalPlainTime
        - JSTemporalPlainYearMonth
        - JSTemporalTimeZone
        - JSTemporalZonedDateTime
        - JSWeakCollection
          - JSWeakMap
          - JSWeakSet
        - JSCollator            // If V8_INTL_SUPPORT enabled.
        - JSDateTimeFormat      // If V8_INTL_SUPPORT enabled.
        - JSDisplayNames        // If V8_INTL_SUPPORT enabled.
        - JSListFormat          // If V8_INTL_SUPPORT enabled.
        - JSLocale              // If V8_INTL_SUPPORT enabled.
        - JSNumberFormat        // If V8_INTL_SUPPORT enabled.
        - JSPluralRules         // If V8_INTL_SUPPORT enabled.
        - JSRelativeTimeFormat  // If V8_INTL_SUPPORT enabled.
        - JSSegmenter           // If V8_INTL_SUPPORT enabled.
        - JSSegments            // If V8_INTL_SUPPORT enabled.
        - JSSegmentIterator     // If V8_INTL_SUPPORT enabled.
        - JSV8BreakIterator     // If V8_INTL_SUPPORT enabled.
        - WasmTagObject
        - WasmGlobalObject
        - WasmInstanceObject
        - WasmMemoryObject
        - WasmModuleObject
        - WasmTableObject
        - WasmSuspenderObject
      - JSProxy
    - FixedArrayBase
      - ByteArray
      - BytecodeArray
      - FixedArray
        - HashTable
          - Dictionary
          - StringTable
          - StringSet
          - CompilationCacheTable
          - MapCache
        - OrderedHashTable
          - OrderedHashSet
          - OrderedHashMap
        - FeedbackMetadata
        - TemplateList
        - TransitionArray
        - ScopeInfo
        - SourceTextModuleInfo
        - ScriptContextTable
        - ClosureFeedbackCellArray
      - FixedDoubleArray
    - PrimitiveHeapObject
      - BigInt
      - HeapNumber
      - Name
        - String
          - SeqString
            - SeqOneByteString
            - SeqTwoByteString
          - SlicedString
          - ConsString
          - ThinString
          - ExternalString
            - ExternalOneByteString
            - ExternalTwoByteString
          - InternalizedString
            - SeqInternalizedString
              - SeqOneByteInternalizedString
              - SeqTwoByteInternalizedString
            - ConsInternalizedString
            - ExternalInternalizedString
              - ExternalOneByteInternalizedString
              - ExternalTwoByteInternalizedString
        - Symbol
      - Oddball
    - Context
      - NativeContext
    - Cell
    - DescriptorArray
    - PropertyCell
    - PropertyArray
    - Code
    - AbstractCode, a wrapper around Code or BytecodeArray
    - Map
    - Foreign
    - SmallOrderedHashTable
      - SmallOrderedHashMap
      - SmallOrderedHashSet
    - SharedFunctionInfo
    - Struct
      - AccessorInfo
      - AsmWasmData
      - PromiseReaction
      - PromiseCapability
      - AccessorPair
      - AccessCheckInfo
      - InterceptorInfo
      - CallHandlerInfo
      - EnumCache
      - TemplateInfo
        - FunctionTemplateInfo
        - ObjectTemplateInfo
      - Script
      - DebugInfo
      - BreakPoint
      - BreakPointInfo
      - CachedTemplateObject
      - StackFrameInfo
      - CodeCache
      - PropertyDescriptorObject
      - PrototypeInfo
      - Microtask
        - CallbackTask
        - CallableTask
        - PromiseReactionJobTask
          - PromiseFulfillReactionJobTask
          - PromiseRejectReactionJobTask
        - PromiseResolveThenableJobTask
      - Module
        - SourceTextModule
        - SyntheticModule
      - SourceTextModuleInfoEntry
    - FeedbackCell
    - FeedbackVector
    - PreparseData
    - UncompiledData
      - UncompiledDataWithoutPreparseData
      - UncompiledDataWithPreparseData
    - SwissNameDictionary
Formats of Object::ptr_:
 Smi:        [31 bit signed int] 0
 HeapObject: [32 bit direct pointer] (4 byte aligned) | 01