addressing Bug #45015 (Issue #316), in r5703.

buf_page_set_accessed_make_young(): New auxiliary function, called by
buf_page_get_zip(), buf_page_get_gen(),
buf_page_optimistic_get_func(). Call ut_time_ms() outside of
buf_pool_mutex. Use cached access_time.

buf_page_set_accessed(): Add the parameter time_ms, so that
ut_time_ms() need not be called while holding buf_pool_mutex.

buf_page_optimistic_get_func(), buf_page_get_known_nowait(): Read
buf_page_t::access_time without holding buf_pool_mutex. This should be
OK, because the field is only used for heuristic purposes.

buf_page_peek_if_too_old(): If buf_pool->freed_page_clock == 0, return
FALSE, so that we will not waste time moving blocks in the LRU list in
the warm-up phase or when the workload fits in the buffer pool.

rb://156 approved by Sunny Bains