Optimize DDL for CHAR(10) to VARCHAR(100)

## Feature Request

Changing a column from a `CHAR(n)` to a `VARCHAR(m)` is now going through a full reorg. However the CHAR is guaranteed to fit in the VARCHAR as long as the charset remains the same and if m>=n.

Here the source is a CHAR and the target is a VARCHAR, but this is likely also true for any other combination of these types and might also be true for VARBINARY etc.

The improvement would be to do this as a metadata only change and only change the actual rows when they are written again.