Introduce FIL_PAGE_ZBLOB_DATA as a synonym for FIL_PAGE_FILE_FLUSH_LSN.

btr_store_big_rec_extern_fields(): Make the assertion about
dict_table_zip_size() more accurate.

buf_LRU_get_free_block(), buf_block_alloc(): Add parameter zip_size.

buf_calc_zblob_page_checksum(): Remove. Replace with page_zip_calc_checksum().

buf_page_init(): Remove parameter zip_size.

buf_page_io_complete(): Add a placeholder for handling compressed pages.

trx_doublewrite_page_inside(): Remove redundant function.

page_zip_write_rec(): Relax an overly tight assertion about blob_no.