A cleanup for: MDEV-18010 Add classes Inet4 and Inet6

- Moving the implementations of class Inet4 and class Inet6 into separate
  files sql_type_inet.h and sql_type_inet.cc, in order to reuse them
  for the INET6 data type and inet function collection.
- Adding a warning in the case when IS_IPV4_MAPPED() and IS_IPV4_COMPAT()
  erroneously gets an IPv4 address instead of the expected IPv6 address.

Author: abarkov

libmysqld/CMakeLists.txt

@@ -116,6 +116,7 @@ SET(SQL_EMBEDDED_SOURCES emb_qcache.cc libmysqld.c lib_sql.cc
            ../sql/sql_mode.cc
            ../sql/sql_type_json.cc
            ../sql/sql_type_geom.cc
+           ../sql/sql_type_inet.cc
            ../sql/table_cache.cc ../sql/mf_iocache_encr.cc
            ../sql/item_inetfunc.cc
            ../sql/wsrep_dummy.cc ../sql/encryption.cc

mysql-test/main/func_misc.result

@@ -1345,6 +1345,9 @@ SELECT IS_IPV4_MAPPED(INET6_ATON('1.2.3.4')),
 IS_IPV4_COMPAT(INET6_ATON('1.2.3.4'));
 IS_IPV4_MAPPED(INET6_ATON('1.2.3.4'))	IS_IPV4_COMPAT(INET6_ATON('1.2.3.4'))
 0	0
+Warnings:
+Warning	1292	Incorrect inet6 value: '\x01\x02\x03\x04'
+Warning	1292	Incorrect inet6 value: '\x01\x02\x03\x04'
 SELECT IS_IPV4_MAPPED(INET6_ATON('::1.2.3.4')),
 IS_IPV4_COMPAT(INET6_ATON('::1.2.3.4'));
 IS_IPV4_MAPPED(INET6_ATON('::1.2.3.4'))	IS_IPV4_COMPAT(INET6_ATON('::1.2.3.4'))

sql/CMakeLists.txt

@@ -137,6 +137,7 @@ SET (SQL_SOURCE
                semisync_master_ack_receiver.cc
                sql_type.cc sql_mode.cc sql_type_json.cc
                sql_type_geom.cc
+               sql_type_inet.cc
                item_windowfunc.cc sql_window.cc
 	       sql_cte.cc
                item_vers.cc