Bug 410189

For convenience it is nice to have a filename proposed from the start, so one can just quickly confirm without having to think and then go testing what one was to test.

The convenience though runs into disappointment when the proposed filename will not be accepted on "Ok", due to conflicts. As can happen if one 2x is fine with the "example.cpp" file name proposed.

Ideally the dialog would be so smart to propose a name which is not already taken, e.g. by adding some number postfix (iterating from first none, then 1 until a non-clashing variant is found). Or have some other source of unique & practically endless naming patterns.