Merge 10.6 into 10.10

The MDEV-29693 conflict resolution is from Monty, as well as is
a bug fix where ANALYZE TABLE wrongly built histograms for
single-column PRIMARY KEY.
Also includes a fix for safe_malloc error reporting.

Other things:
- Copied main.log_slow from 10.4 to avoid mtr issue

Disabled test:
- spider/bugfix.mdev_27239 because we started to get
  +Error	1429 Unable to connect to foreign data source: localhost
  -Error	1158 Got an error reading communication packets
- main.delayed
  - Bug#54332 Deadlock with two connections doing LOCK TABLE+INSERT DELAYED
    This part is disabled for now as it fails randomly with different
    warnings/errors (no corruption).

include/my_alloc.h

@@ -53,6 +53,10 @@ typedef struct st_mem_root
   unsigned short first_block_usage;
   unsigned short flags;
 
+#ifdef PROTECT_STATEMENT_MEMROOT
+  int read_only;
+#endif
+
   void (*error_handler)(void);
 
   PSI_memory_key psi_key;