MDEV-8865 Wrong field type or metadata for COALESCE(signed_int_column, unsigned_int_column)

Item_func_hybrid_field_type did not return correct field_type(), cmp_type()
and result_type() in some cases, because cached_result_type and
cached_field_type were set in independent pieces of the code and
did not properly match to each other.
Fix:
- Removing Item_func_hybrid_result_type
- Deriving Item_func_hybrid_field_type directly from Item_func
- Introducing a new class Type_handler which guarantees that
  field_type(), cmp_type() and result_type() are always properly synchronized
  and using the new class in Item_func_hybrid_field_type.

Author: Alexander Barkov

libmysqld/CMakeLists.txt

@@ -104,6 +104,7 @@ SET(SQL_EMBEDDED_SOURCES emb_qcache.cc libmysqld.c lib_sql.cc
            ../sql/sql_explain.cc ../sql/sql_explain.h
            ../sql/sql_analyze_stmt.cc ../sql/sql_analyze_stmt.h
            ../sql/compat56.cc
+           ../sql/sql_type.cc ../sql/sql_type.h
            ../sql/table_cache.cc ../sql/mf_iocache_encr.cc
            ../sql/item_inetfunc.cc
            ../sql/wsrep_dummy.cc ../sql/encryption.cc

mysql-test/include/func_hybrid_type.inc

@@ -0,0 +1,81 @@
+# "mtr --ps" returns different values in "Max length"
+--disable_ps_protocol
+--enable_metadata
+--vertical_results
+SELECT
+  a                                         AS ___________a,
+  CASE WHEN a IS NOT NULL THEN a END        AS case_______a,
+  CASE WHEN a IS NOT NULL THEN a ELSE a END AS case_____a_a,
+  COALESCE(a)                               AS coalesce___a,
+  COALESCE(a, a)                            AS coalesce_a_a,
+  IF(a IS NULL, a, a)                       AS if_______a_a,
+  IFNULL(a, a)                              AS ifnull___a_a,
+  LEAST(a, a)                               AS least____a_a,
+  GREATEST(a, a)                            AS greatest_a_a,
+  b                                         AS ___________b,
+  CASE WHEN a IS NOT NULL THEN b END        AS case_______b,
+  CASE WHEN a IS NOT NULL THEN b ELSE b END AS case_____b_b,
+  COALESCE(b)                               AS coalesce___b,
+  COALESCE(b, b)                            AS coalesce_b_b,
+  IF(a IS NULL, b, b)                       AS if_______b_b,
+  IFNULL(b, b)                              AS ifnull___b_b,
+  LEAST(b, b)                               AS least____b_b,
+  GREATEST(b, b)                            AS greatest_b_b
+FROM t1;
+SELECT
+  CASE WHEN a IS NOT NULL THEN a ELSE b END AS case_____a_b,
+  CASE WHEN a IS NOT NULL THEN b ELSE a END AS case_____b_a,
+  COALESCE(a, b)                            AS coalesce_a_b,
+  COALESCE(b, a)                            AS coalesce_b_a,
+  IF(a IS NULL, a, b)                       AS if_______a_b,
+  IF(a IS NULL, b, a)                       AS if_______b_a,
+  IFNULL(a, b)                              AS ifnull___a_b,
+  IFNULL(b, a)                              AS ifnull___b_a,
+  LEAST(a, b)                               AS least____a_b,
+  LEAST(b, a)                               AS least____b_a,
+  GREATEST(a, b)                            AS greatest_a_b,
+  GREATEST(b, a)                            AS greatest_b_a
+FROM t1;
+--horizontal_results
+--disable_metadata
+--enable_ps_protocol
+CREATE TABLE t2 AS
+SELECT
+  a                                         AS ___________a,
+  CASE WHEN a IS NOT NULL THEN a END        AS case_______a,
+  CASE WHEN a IS NOT NULL THEN a ELSE a END AS case_____a_a,
+  COALESCE(a)                               AS coalesce___a,
+  COALESCE(a, a)                            AS coalesce_a_a,
+  IF(a IS NULL, a, a)                       AS if_______a_a,
+  IFNULL(a, a)                              AS ifnull___a_a,
+  LEAST(a, a)                               AS least____a_a,
+  GREATEST(a, a)                            AS greatest_a_a,
+  b                                         AS ___________b,
+  CASE WHEN a IS NOT NULL THEN b END        AS case_______b,
+  CASE WHEN a IS NOT NULL THEN b ELSE b END AS case_____b_b,
+  COALESCE(b)                               AS coalesce___b,
+  COALESCE(b, b)                            AS coalesce_b_b,
+  IF(a IS NULL, b, b)                       AS if_______b_b,
+  IFNULL(b, b)                              AS ifnull___b_b,
+  LEAST(b, b)                               AS least____b_b,
+  GREATEST(b, b)                            AS greatest_b_b
+FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+CREATE TABLE t2 AS
+SELECT
+  CASE WHEN a IS NOT NULL THEN a ELSE b END AS case_____a_b,
+  CASE WHEN a IS NOT NULL THEN b ELSE a END AS case_____b_a,
+  COALESCE(a, b)                            AS coalesce_a_b,
+  COALESCE(b, a)                            AS coalesce_b_a,
+  IF(a IS NULL, a, b)                       AS if_______a_b,
+  IF(a IS NULL, b, a)                       AS if_______b_a,
+  IFNULL(a, b)                              AS ifnull___a_b,
+  IFNULL(b, a)                              AS ifnull___b_a,
+  LEAST(a, b)                               AS least____a_b,
+  LEAST(b, a)                               AS least____b_a,
+  GREATEST(a, b)                            AS greatest_a_b,
+  GREATEST(b, a)                            AS greatest_b_a
+FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;