btr_block_get(): New function to return buf_block_t.

btr_page_alloc(), buf_page_get_release_on_io(), buf_page_get_gen(),
buf_page_create(), fseg_create(), fseg_create_general(): Return buf_block_t.

buf_page_get_known_nowait(): Expect buf_block_t instead of buf_frame_t.

buf_frame_get_newest_modification(): Replace with
buf_block_get_newest_modification().

buf_page_dbg_add_level(): Replace with buf_block_dbg_add_level().

buf_block_get_zip_size(): New function.

buf_block_get_page_zip(): Reintroduce.

recv_recover_page(): Replace page, space, page_no with block.

ibuf_bitmap_page_init(): Replace page, zip_size with block.

ibuf_parse_bitmap_init(): Remove the parameter zip_size.

btr_search_drop_page_hash_index(): Replace page with block.