create json value from string with binary charset should report error

[YangKeao]

Enhancement

In MySQL 5.7, creating a json key from the blob value will give an error:

create table t (s varchar(255), b blob);
insert into t values ("a string", X'ABCD');
insert into t values ("b string", X'DCBA');

select json_objectagg(b,s) from t;

Will give an error: ERROR 3144 (22032): Cannot create a JSON value from a string with CHARACTER SET 'binary'..

In TiDB, it will give: {"\ufffd\ufffd": "a string", "ܺ": "b string"}