[Optimize] Support deriving a new ElementBinaryReader from ElementBin…

…aryReader.

Described as title. With this feature, we can construct a new ElementBinaryReader and use it in an asynchronous thread to perform some necessary parsing operations. This enables multi-threaded parallel parsing of Element Templates, thereby optimizing performance.

issue:m-6083199326
AutoSubmit:True

core/runtime/vm/lepus/base_binary_reader.h

@@ -160,7 +160,6 @@ class BaseBinaryReader : public BinaryReader {
 #endif
   tasm::CompileOptions compile_options_;
 
- private:
   std::vector<base::String> string_list_;
 };
 

core/template_bundle/template_codec/binary_decoder/element_binary_reader.cc

@@ -396,8 +396,20 @@ bool ElementBinaryReader::ConstructElement(ElementSectionEnum section_type,
   return true;
 }
 
-// These are the APIs used for decoding data and return element infos:
+std::unique_ptr<ElementBinaryReader>
+ElementBinaryReader::DeriveElementBinaryReader() {
+  auto reader =
+      std::make_unique<ElementBinaryReader>(stream_->DeriveInputStream());
+  reader->element_templates_router_ = element_templates_router_;
+  reader->string_key_parsed_styles_router_ = string_key_parsed_styles_router_;
+
+  reader->compile_options_ = compile_options_;
+  reader->string_list_ = string_list();
 
+  return reader;
+}
+
+// These are the APIs used for decoding data and return element infos:
 // Lazy decode. Only decode templates router. The
 // decoding of the template waits until it is actually needed.
 bool ElementBinaryReader::DecodeElementTemplatesRouter() {

core/template_bundle/template_codec/binary_decoder/element_binary_reader.h

@@ -47,6 +47,8 @@ class ElementBinaryReader : public LynxBinaryBaseCSSReader {
   std::shared_ptr<ElementTemplateInfo> DecodeTemplatesInfoWithKey(
       const std::string& key);
 
+  std::unique_ptr<ElementBinaryReader> DeriveElementBinaryReader();
+
  protected:
   // These are the APIs used for decoding data into fiber elements.
   virtual bool DecodeElementChildrenSection(fml::RefPtr<FiberElement>& element,