Incremental tables with varchar columns get bumped to varchar 256

[gshank]

Current Behavior

In #10362 we fixed a bug where incremental tables with varchar columns and a contract were getting the varchar columns increased to size 256, which didn't match the column. In the interests of getting it fixed for the most egregious case, we limited
the execution of expand_target_columns_types to non-contracted incremental tables, however there is still probably a problem for non-contracted tables getting varchar columns changed to 256 because of awkwardnesses in the way the code works with varchar column sizes.

Expected Behavior

Incremental table varchar columns are not bumped to 256 when it's not needed.

Steps to Reproduce

Relevant log output

Additional Context