Refactor: based: cib_get_operation_id() -> cib_get_operation()

Currently, we get the operation's integer ID (more accurately its index
in an internal array) and then pass that index to various getter
functions.

However, those getter functions are all very simple. If we remove the
getters, we can simplify the code by returning a const pointer to the
cib_operation_t struct and accessing its members directly -- thus
eliminating the "call_type" integer variable.

Continue returning a legacy RC rather than a const cib_operation_t *
from cib_get_operation(), to simplify error handling in callers.

Closes T658

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>