Steps to reproduce the issue

Create a JSON string for the "special" key of the #__content_types table's table field that uses longer names for the dbtable or key than the JSON used in default installation, or includes configuration options.

Expected result

That the database update won't error

Actual result

Database errors, as the field is defined as VARCHAR(255) on MySQL

System information (as much as possible)

MySQL database, Joomla! 3.8.10

Additional comments

The largest current entry for the table field is for Newsfeeds (type_alias com_newsfeeds.newsfeed), at 227 characters. The field is created as VARCHAR(255). I am using a prefixed surrogate key (so longer than just id) and my component table is namespaced (e.g. #__vendor_tablename), and together they exceed the 255 character limit.

Also, I notice that there are "config":"array()" keys in the JSON. One configuration option in com_contenthistory is ignore_request, set to a default of true. Any configuration options used would likely push the string length over the 255 character limit.

I'd submit a PR, but don't have a good feel for what the field size should be.