src: split BlobSerializer/BlobDeserializer

This patch splits BlobSerializer and BlobDeserializer out of
SnapshotSerializer and SnapshotDeserializer. The child classes
can implement serialization methods for custom types on top
of BlobSerializer/BlobDeserializer for conversions between
native types and binary blobs. This allows us to reuse the
classes for other cases (e.g. SEA blobs).

PR-URL: #47458
Reviewed-By: Darshan Sen <raisinten@gmail.com>

Author: joyeecheung

src/env.h

@@ -534,6 +534,7 @@ struct SnapshotData {
   bool Check() const;
   static bool FromFile(SnapshotData* out, FILE* in);
   static bool FromBlob(SnapshotData* out, const std::vector<char>& in);
+  static bool FromBlob(SnapshotData* out, std::string_view in);
   static const SnapshotData* FromEmbedderWrapper(
       const EmbedderSnapshotData* data);
   EmbedderSnapshotData::Pointer AsEmbedderWrapper() const;