For 2.1.8 (this task), deprecate (via doxygen comments) public API access to:

• struct pe_action_wrapper_s
• struct pe_action_s (except as the opaque type alias pcmk_action_t)
• pcmk_on_fail_text()
• pcmk_action_text()
• pcmk_parse_action()
• enum pe_action_flags
• enum action_fail_response
• enum action_tasks

For 3.0.0 (T797), we can make those internal, and rename struct pe_action_s to struct pcmk__action for type aliasing purposes.