Copying form of cholmod_*_xtype

[rayegun]

Currently the semantics of cholmod_*_xtype are not great since it mutates the data type of an object. It would be nicer in most cases to have cholmod_*_copy_xtype which returns a new object with the new data type. This would avoid the double memory allocation of cholmod_*_copy followed by cholmod_*_xtype.

[DrTimothyAldenDavis]

That would be useful. I'll consider it for CHOLMOD 5.2 (I would bump the 2nd digit from 1 to 2, because this would be a new addition to the user-visible API). I'd like to keep CHOLMOD 5.1.1 as-is for SuiteSparse 7.5.0.