MDEV-34705: Binlog-in-engine: Binlog reader to read whole page at a time

Instead of returning only one chunk at a time, make
ha_innodb_binlog_reader::read_data() try to read all chunks on the page.
This reduces the number of times each reader has to latch pages in the page
fifo, which contends for a global mutex also shared with the writer.

Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

sql/handler.h

@@ -5964,7 +5964,12 @@ public:
     support legacy SHOW BINLOG EVENTS.
   */
   virtual int init_legacy_pos(const char *filename, ulonglong offset) = 0;
-
+  /*
+    Can be called after init_gtid_pos() or init_legacy_pos() to make the reader
+    stop (return EOF) at the end of the binlog file. Used for SHOW BINLOG
+    EVENTS, which has a file-based interface based on legacy file name.
+  */
+  virtual void enable_single_file() = 0;
   int read_log_event(String *packet, uint32_t ev_offset, size_t max_allowed);
 };