fix gcc 8 compiler warnings

There were two newly enabled warnings:
1. cast for a function pointers. Affected sql_analyse.h, mi_write.c
   and ma_write.cc, mf_iocache-t.cc, mysqlbinlog.cc, encryption.cc, etc

2. memcpy/memset of nontrivial structures. Fixed as:
* the warning disabled for InnoDB
* TABLE, TABLE_SHARE, and TABLE_LIST got a new method reset() which
  does the bzero(), which is safe for these classes, but any other
  bzero() will still cause a warning
* Table_scope_and_contents_source_st uses `TABLE_LIST *` (trivial)
  instead of `SQL_I_List<TABLE_LIST>` (not trivial) so it's safe to
  bzero now.
* added casts in debug_sync.cc and sql_select.cc (for JOIN)
* move assignment method for MDL_request instead of memcpy()
* PARTIAL_INDEX_INTERSECT_INFO::init() instead of bzero()
* remove constructor from READ_RECORD() to make it trivial
* replace some memcpy() with c++ copy assignments

unittest/sql/mf_iocache-t.cc

@@ -49,6 +49,12 @@ uint encryption_key_get_func(uint, uint, uchar* key, uint* size)
   return 0;
 }
 
+uint encryption_ctx_size_func(unsigned int, unsigned int)
+{
+  return MY_AES_CTX_SIZE;
+}
+
+
 #ifdef HAVE_EncryptAes128Gcm
 enum my_aes_mode aes_mode= MY_AES_GCM;
 #else
@@ -72,7 +78,7 @@ struct encryption_service_st encryption_handler=
 {
   encryption_key_get_latest_version_func,
   encryption_key_get_func,
-  (uint (*)(unsigned int, unsigned int))my_aes_ctx_size,
+  encryption_ctx_size_func,
   encryption_ctx_init_func,
   my_aes_crypt_update,
   my_aes_crypt_finish,