Fix Migration 145 on MSSQL if varchar is changed to nvarchar

[zeripath]

Some versions of MSSQL will fail on migration v145 because there is a constraint failure.

This PR drops the constraints on the language column prior to its alteration and then recreates them with sync.

Fix #12441
Fix #13013

Signed-off-by: Andrew Thornton art27@cantab.net

[zeripath]

Make lg-tm work

[lafriks]

Still fails with error:

mssql: The operation failed because an index or statistics with name 'UQE_language_stat_s' already exists on table 'language_stat'.

[zeripath]

It looks like:

SELECT Name FROM SYS.DEFAULT_CONSTRAINTS WHERE 
	PARENT_OBJECT_ID = OBJECT_ID('language_stat') AND
	PARENT_COLUMN_ID IN (SELECT column_id FROM sys.columns
		WHERE lower(NAME) = 'language' AND object_id = OBJECT_ID('language_stat')

isn't finding the unique constraint. Which is weird

[zeripath]

OK I'm going to try a different query...

SELECT i.name AS Name
	FROM sys.indexes i INNER JOIN sys.index_columns ic
		ON i.index_id = ic.index_id AND i.object_id = ic.object_id
	INNER JOIN sys.tables AS t 
		ON t.object_id = i.object_id
	INNER JOIN sys.columns c
		ON t.object_id = c.object_id AND ic.column_id = c.column_id
	WHERE t.name = 'language_stat' AND c.name = 'language'

[zeripath]

OK that finally appears to work.