Test copying a large file

[jaakkor2]

Test issues

• cp(file,file-copy) broken for >2GB files #14574 (fixed)
• IOError from cp with large file on Windows #30723 (copy failure on Windows when filesize is >2 GB).

#30989 warns that CI might not like big files, let's see.

[KristofferC]

Note that testing this was explicitly mentioned in #30989 (comment) and decided against. Just pointing it out for reference.

[imciner2]

Please don't test it this way. Testing using multi GB files would not be good for low memory bandwidth systems (such as some ARM boards) since it would make the already painfully-slow unit testing even slower, and could possibly lead to out of space errors on smaller devices because there are now multiple large files being created.

[jaakkor2]

Testing for #30723 needed, but based on comments this is not the way.