create a function to create file with forced permissions

[sylvestre]

No description provided.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cp/acl. tests/cp/acl is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cp/preserve-mode. tests/cp/preserve-mode is passing on 'main'. Maybe you have to rebase?

[ChrisDryden]

I'm curious where the justification for this comes from?

I have been reading up on these options and what the default File create does and I think the default behaviour is mode o666 and when running commands to compare what is used by the gnu commands the only command that I could find of these that used a more restrictive mode was cp and that the other ones do not have this behaviour

for example for gnu touch which matches main:

-rw-rw-rw-

Which is now:

-rw-------

But the two gnu compatibility improvements I do see in the PR is that this is a step forward with the right behavior for cp and the sort file creation was missing the truncate flag.