fix generated column check in information_schema extra field

[amyangfei]

in mysql5.7, Extra Fields include:

auto_increment for columns that have the AUTO_INCREMENT attribute.
on update CURRENT_TIMESTAMP for TIMESTAMP or DATETIME columns that have the ON UPDATE CURRENT_TIMESTAMP attribute.
VIRTUAL GENERATED or VIRTUAL STORED for generated columns.

in mysql8.0, Extra Fields include:

auto_increment for columns that have the AUTO_INCREMENT attribute.
on update CURRENT_TIMESTAMP for TIMESTAMP or DATETIME columns that have the ON UPDATE CURRENT_TIMESTAMP attribute.
VIRTUAL GENERATED or VIRTUAL STORED for generated columns.
DEFAULT_GENERATED for columns that have an expression default value.

I also checked mariadb 10.2, 10.3 have VIRTUAL GENERATED and DEFAULT_GENERATED too in extra too.

Before this pr, mydumper uses like '%GENERATED%' to filter generated column, which will have false positive (treat non-generated column as generated column). We can use more accurate match rule for the generated column.

[kennytm]

LGTM

[csuzhangxc]

LGTM