Refactors raw2trace_t for trace-buffer-driven use rather than file-driven use:
- Separates out a new function process_next_thread_buffer() from process_thread_file().
- check_thread_file() now puts the header back, so it can be universally processed in process_next_thread_buffer() (this seek is just once per traced thread so there are no performance concerns like in PR #2749).
- The thread footer is now written out in on_thread_end(), leaving process_thread_file() only performing file-specific actions.
- Removes {un,}read_from_thread_file(), merging them into {unread,get}_next_entry().
- Marks key functions as virtual and protected for subclass support.
Issue: #3230 (closed)