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).

sql/opt_histogram_json.h

@@ -64,7 +64,7 @@
   are not mapped to any UTF8 character.
 */
 
-class Histogram_json_hb : public Histogram_base
+class Histogram_json_hb final : public Histogram_base
 {
   size_t size; /* Number of elements in the histogram */
 
@@ -93,8 +93,8 @@ public:
   static constexpr const char* JSON_NAME="histogram_hb";
 
   bool parse(MEM_ROOT *mem_root, const char *db_name, const char *table_name,
-             Field *field, Histogram_type type_arg,
-             const char *hist_data, size_t hist_data_len) override;
+             Field *field, const char *hist_data,
+             size_t hist_data_len) override;
 
   void serialize(Field *field) override;
 
@@ -121,7 +121,6 @@ public:
   {
     return (uint)size;
   }
-
   void init_for_collection(MEM_ROOT *mem_root, Histogram_type htype_arg,
                            ulonglong size) override;