MDEV-30987 main.alter_table_online times out with view-protocol
disabie view-protocol for certain places:
1. While a transaction is in progress: a view gets locked for a
transaction duration, so DROP VIEW from a servicing conneciton
deadlocks. We can't just disable servicing connection, as
CREATE VIEW and DROP VIEW commit implicitly.
2. For querying Opened_table_definitions: the actual query executed
is `SELECT * FROM mysqltest_tmp_v`, then the view is dropped
Online alter and replication paths differ quite noticeably. It's time to
fix the mess. Online alter has to unpack the old table's data
(here conv_table), and then convert, while replication requires more
sophisticated track: handle possible conversions, treat extra replica
fields, and carefully deduce master's record length.
* Extract unpack_field.
* handle the unpacking progress through a state machine presented by
Unpack_record_state struct.
* Stick most of the online alter unpacking together under a single
conditional branch.
MDEV-30949 Direct leak in binlog_online_alter_end_trans
when committing a big transaction, online_alter_cache_log creates a cache
file. It wasn't properly closed, which was spotted by a memory leak from
my_register_filename. A temporary file also remained open.
Binlog wasn't affected by this, since it features its own file management.
A proper closing is calling close_cached_file. It deinits io_cache and
closes the underlying file. After closing, the file is expected to be
deleted automagically.
