For 2.1.8 (this task), deprecate (via doxygen comments) direct access to all members of `struct pe_node_s` and `struct pe_node_shared_s`.
We will need new public APIs that SBD can be updated to use (T794) instead of direct access. We will need to keep the members SBD uses around until we no longer support any OSes shipping an older version.
* `struct pe_node_s`
** For 3.0.0 (T795), we can rename it to something like `struct pcmk__scored_node`, and replace all members except `details` with a `void *private` member pointing to a new internal struct for the replaced members
* `struct pe_node_shared_s`
** Define new public APIs for "is node online/pending/unclean/shutdown/maintenance" that get the value of the named members
** Define a new public API to get the value of `running_rsc` (or alternatively, a "foreach running_rsc" API)
** For 3.0.0, we can rename it to `struct pcmk__node`, and replace all members //except// those above with a `void *private` member pointing to a new internal struct for the replaced members
* `enum node_type`: for 2.1.8, we can deprecate public access to this; for 3.0.0, we can make it internal