Add 'alter collation' API support

[tznind]

This would enable HicServices/RDMP#1288 and would be generically useful.

• MySql syntax - https://stackoverflow.com/questions/1294117/how-to-change-collation-of-database-table-column
• Sql Server syntax
• PostgresSql syntax
• Oracle syntax

[tznind]

Added complication in Sql Server if the column is part of the primary key you have to drop and recreate the primary key while doing the collation change (may also be the case for other DBMS too).