支持用户对bvar名称做自定义的归一化处理

**需求背景**
有些用户自定义名称可能有特殊含义，比如 "3AE5D89"，会被规化成 "3_AE_5_D_89"，这种规一化会对展现，以及监控等配置造成困扰。

**Describe the solution you'd like (描述你期望的解决方法)**
增加一个全局的name_normalization_func，默认值为to_underscored_name

typedef void (*name_normalization_func)(std::string* name, const base::StringPiece& src);
name_normalization_func g_name_normalization = to_underscored_name;

如果用户需要对bvar名称做自定义的归一化处理，只需要调用set_name_normalization_func
void set_name_normalization_func(name_normalization_func func_name);

Start by locating bvar's existing name normalization path and the to_underscored_name function. Trace how bvar names are created, then assess where the global name_normalization_func and set_name_normalization_func entry point belong; done means callers can provide custom normalization while the default behavior remains unchanged.

Written by the indexing model from the issue text.