InnoDB crash recovery buffers redo log records in a hash table.
The function recv_read_in_area() would pick a random hash bucket
and then try to submit read requests for a few nearby pages.
Let us replace the recv_sys.addr_hash with a std::map, which will
automatically be iterated in sorted order.

recv_sys_t::pages: Replaces recv_sys_t::addr_hash, recv_sys_t::n_addrs.

recv_sys_t::recs: Replaces most of recv_addr_t.

recv_t: Encapsulate a raw singly-linked list of records. This reduces
overhead compared to std::forward_list. Storage and cache overhead,
because the next-element pointer also points to the data payload.
Processing overhead, because recv_sys_t::recs_t::last will point to
the last record, so that recv_sys_t::add() can append straight to the
end of the list.

RECV_PROCESSED, RECV_DISCARDED: Remove. When a page is fully processed,
it will be deleted from recv_sys.pages.

recv_sys_t::trim(): Replaces recv_addr_trim().

recv_sys_t::add(): Use page_id_t for identifying pages.

recv_fold(), recv_hash(), recv_get_fil_addr_struct(): Remove.

recv_read_in_area(): Simplify the iteration.