STYLE: Replace SetSize/Index calls in tests with `region{ index, size }`

[N-Dekker]

Replaced code like:

RegionType region;
region.SetSize(size);
region.SetIndex(index);

With the shorter equivalent, RegionType region{ index, size };

Using Notepad++, Replace in Files:

Find what: ^( [ ]+)(\w.*Region[^ ]*)([ ]+)(\w+);\r\n\1\4\.SetSize\((\w+)\);\r\n\1\4\.SetIndex\((\w+)\);
Replace with: $1$2$3$4{ $6, $5 };
Find what: ^( [ ]+)(\w.*Region[^ ]*)([ ]+)(\w+);\r\n\1\4\.SetIndex\((\w+)\);\r\n\1\4\.SetSize\((\w+)\);
Replace with: $1$2$3$4{ $5, $6 };
Filters: itk*Test*.cxx
[v] Match case
(*) Regular expression

[N-Dekker]

@thewtex This pull request is only a style improvement of the unit tests. So I think it won't harm to have it merged with ITK 5.4. I like this PR very much, but it's not very urgent, of course. What do you think? 🤷