The null_free_inline_type is a concept for fields, representing:
1. null checked fields
2. flat field with no null marker in layout

These two concepts were grouped together before, but with the null restricted type proposal, they are now separate. As a result, hotspot should split the corresponding functions is_null_free_inline_type on fieldDescriptor to different functions. (In addition, with the addition of ACC_NULL_CHECKED 0x200, we might remove the fieldFlag for null_free_inline_type later)