0027000: Invalid result of ShapeUpgrade_UnifySameDomain

0027000: Invalid result of ShapeUpgrade_UnifySameDomain

This commit is a cherry-pick of commits from master related to ShapeUpgrade_UnifySameDomain that fix bug 27000.
Note that picked commits was backported from 7.0.0 to 6.9.0 so changes in header file moved to CDL.

Here is a set of picked commits:
1)SHA-1: f7d7054
0026489: The class ShapeUpgrade_UnifySameDomain provides the results that are wrong or difficult to explain.
1)SHA-1: f2d685a
0026572: Error in ShapeUpgrade_UnifySameDomain algorithm: can not merge two edges in customer's shape
2)SHA-1: dd2f1b7
0026244: Destructive results of simplification with DRAW command 'unifysamedom' after intersection of two complex models
3)SHA-1: 6a0c0b1
0026635: UnifySameDomain loses internal edges
4)SHA-1: cef6867
0026488: The class ShapeUpgrade_UnifySameDomain is not documented.