Description:
============
In row based replication, when replicating from a table with
a field with character set set to UTF8mb3 to the same table
with the same field set to character set UTF8mb4 I get a
confusing error message:

For VARCHAR: VARCHAR(1) 'utf8mb3' to VARCHAR(1) 'utf8mb4'

"Column 0 of table 'test.t1' cannot be converted from type
'varchar(3)' to type 'varchar(1)'"

Similar issue with CHAR type as well.

Issue with respect to BLOB types:

For BLOB: LONGBLOB to TINYBLOB - Error message displays
incorrect blob type.

"Column 0 of table 'test.t1' cannot be converted from type
'tinyblob' to type 'tinyblob'"

Analysis:
=========
In Row based replication charset information is not sent as
part of metadata from master to slave.

For VARCHAR field its character length is converted into
equivalent octets/bytes and stored internally. At the time
of displaying the data to user it is converted back to
original character length.

For example:
VARCHAR(2)- utf8mb3 is stored as:2*3 = VARCHAR(6)
At the time of displaying it to user
VARCHAR(6)- charset utf8mb3:6/3= VARCHAR(2).

At present the internally converted octect length is sent
from master to slave with out providing the charset
information. On slave side if the type conversion fails
'show_sql_type' function is used to get the type specific
information from metadata. Since there is no charset
information is available the filed type is displayed as
VARCHAR(6).

This results in confused error message.

For CHAR fields
CHAR(1)- utf8mb3 - CHAR(3)
CHAR(1)- utf8mb4 - CHAR(4)

'show_sql_type' function which retrieves type information
from metadata uses (bytes/local charset length) to get
actual character length. If slave's chaset is 'utf8mb4' then

CHAR(3/4)-->CHAR(0)
CHAR(4/4)-->CHAR(1).

This results in confused error message.

Analysis for BLOB type issue:

BLOB's length is represented in two forms.
1. Actual length
i.e
  (length < 256) type= MYSQL_TYPE_TINY_BLOB;
  (length < 65536) type= MYSQL_TYPE_BLOB; ...

2. packlength - The number of bytes used to represent the
length of the blob
  1- tinyblob
  2- blob ...

In row based replication only the packlength is written in
the binary log. On the slave side this packlength is
interpreted as actual length of the blob.  Hence the length
is always < 256 and the type is displayed as tiny blob.

Fix:
===
For CHAR and VARCHAR fields display their length in bytes
for both source and target fields. For target field display
the charset information if it is relevant.

For blob type changed the code to use the packlength and
display appropriate blob type in error message.