Move vers_type_timestamp within the CC file

It's a virtual method and it can't be inlined anyway. This allows type
plugins (mysql_json in particular) to use Type_handler_blob and / or
subclass it, without needing to explicitly expose the
vers_type_timestamp object.

sql/sql_type.cc

@@ -6958,6 +6958,24 @@ bool Type_handler_string_result::
 
 /***************************************************************************/
 
+const Vers_type_handler* Type_handler_temporal_result::vers() const
+{
+  return &vers_type_timestamp;
+}
+
+const Vers_type_handler* Type_handler_string_result::vers() const
+{
+  return &vers_type_timestamp;
+}
+
+const Vers_type_handler* Type_handler_blob_common::vers() const
+
+{
+  return &vers_type_timestamp;
+}
+
+/***************************************************************************/
+
 uint Type_handler::Item_time_precision(THD *thd, Item *item) const
 {
   return MY_MIN(item->decimals, TIME_SECOND_PART_DIGITS);

sql/sql_type.h

@@ -3498,7 +3498,7 @@ class Vers_type_timestamp: public Vers_type_handler
                         const Column_definition *row_start,
                         const Column_definition *row_end) const;
 };
-extern MYSQL_PLUGIN_IMPORT Vers_type_timestamp vers_type_timestamp;
+extern Vers_type_timestamp vers_type_timestamp;
 
 
 class Vers_type_trx: public Vers_type_handler
@@ -5249,7 +5249,7 @@ class Type_handler_temporal_result: public Type_handler
   bool Item_func_mul_fix_length_and_dec(Item_func_mul *) const override;
   bool Item_func_div_fix_length_and_dec(Item_func_div *) const override;
   bool Item_func_mod_fix_length_and_dec(Item_func_mod *) const override;
-  const Vers_type_handler *vers() const override { return &vers_type_timestamp; }
+  const Vers_type_handler *vers() const override;
 };
 
 
@@ -5416,7 +5416,7 @@ class Type_handler_string_result: public Type_handler
   bool Item_func_mul_fix_length_and_dec(Item_func_mul *) const override;
   bool Item_func_div_fix_length_and_dec(Item_func_div *) const override;
   bool Item_func_mod_fix_length_and_dec(Item_func_mod *) const override;
-  const Vers_type_handler *vers() const override { return &vers_type_timestamp; }
+  const Vers_type_handler *vers() const override;
 };
 
 
@@ -7039,7 +7039,7 @@ class Type_handler_blob_common: public Type_handler_longstr
                                    const Bit_addr &bit,
                                    const Column_definition_attributes *attr,
                                    uint32 flags) const override;
-  const Vers_type_handler *vers() const override { return &vers_type_timestamp; }
+  const Vers_type_handler *vers() const override;
 };