Add comment property to database classes

[michaelarnauts]

A database can contain comments on the columns and the table itself. The comment of the columns can be read out trough the ColumnSchema class, but the comment on the table itself isn't.

Is this something that is open for inclusion in Yii 2? This is a bit related to #6093, but that PR wasn't accepted, so I want to avoid to work on this if it won't be accepted.

This could be used to generate usefull phpdoc with Gii based on the database comments.

[samdark]

I'm OK having it.

[dynasource]

me too. Table comments are useful, like i.e. for sorting in Navicat.

[samdark]

https://github.com/yiisoft/yii2/pull/13162

[terabytesoftw]

done.