MDEV-35211: Make VEC_FromText return VECTOR type instead of VARBINARY

VEC_FROMTEXT() was incorrectly inheriting its type handler from
Item_str_func, causing it to be identified as VARBINARY. This led
to incorrect column types (VARBINARY instead of VECTOR) when using
CREATE TABLE ... AS SELECT.

This change:
- Overrides type_handler() in Item_func_vec_fromtext to return
  type_handler_vector.
- Overrides create_field_for_create_select() to ensure the field is
  created correctly using the vector type handler during table
  creation.
- Adds a regression test in vector_funcs.test to verify that
  CREATE TABLE ... AS SELECT now correctly creates a column of
  type VECTOR.

mysql-test/main/vector_funcs.result

@@ -265,4 +265,14 @@ drop table t;
 #
 select vec_distance(value(key_cache_name), 0x30303030) from information_schema.key_caches;
 ERROR HY000: Cannot determine distance type for VEC_DISTANCE, index is not found
+#
+# MDEV-35211: VEC_FromText does not return vector type but varbinary
+#
+create table t as select vec_fromtext('[1,2,3]') as v;
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `v` vector(3) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci
+drop table t;
 # End of 11.8 tests

mysql-test/main/vector_funcs.test

@@ -153,4 +153,11 @@ drop table t;
 --error ER_VEC_DISTANCE_TYPE
 select vec_distance(value(key_cache_name), 0x30303030) from information_schema.key_caches;
 
+--echo #
+--echo # MDEV-35211: VEC_FromText does not return vector type but varbinary
+--echo #
+create table t as select vec_fromtext('[1,2,3]') as v;
+show create table t;
+drop table t;
+
 --echo # End of 11.8 tests

sql/item_vectorfunc.h

@@ -21,6 +21,7 @@
 #include "item.h"
 #include "lex_string.h"
 #include "item_func.h"
+#include "sql_type_vector.h"
 
 class Item_func_vec_distance: public Item_real_func
 {
@@ -94,6 +95,10 @@ public:
   bool fix_length_and_dec(THD *thd) override;
   Item_func_vec_fromtext(THD *thd, Item *a);
   String *val_str(String *buf) override;
+  const Type_handler *type_handler() const override
+  { return &type_handler_vector; }
+  Field *create_field_for_create_select(MEM_ROOT *root, TABLE *table) override
+  { return create_table_field_from_handler(root, table); }
   LEX_CSTRING func_name_cstring() const override
   {
     static LEX_CSTRING name= { STRING_WITH_LEN("VEC_FromText") };