cat: Handle all flags correctly

[BenWiederhake]

This PR fixes several bugs:

• Accept repeated flags, just like GNU cat does
• Make sure that -b overrides -n but not the other way around, just like GNU cat does
• Accept and ignore the -u flag, just like GNU cat does

This is work towards #5998. Note that this is the first time that args_override_self is correct.

I'm surprised that we already passed the GNU tests before!

[tertsdiepraam]

I'm thinking now that I was confused with infer_long_args which I added to everything and maybe we didn't do it for args_override_self, because like you already noticed, it takes some effort to check whether it is actually right. Anyway, great work on fixing this up :)

[BenWiederhake]

Changes since last push:

• Removed misleading comment. Thanks @tertsdiepraam!
• Rebased on current main.

[tertsdiepraam]

I'm a bit torn on the test_ prefix. It's good for consistency now, but I'm thinking we could remove the test_ prefix everywhere later. But it's really not important, just something I wanted to bring up at some point.

Should not be a blocker to merge this though.

[cakebaker]

@tertsdiepraam Yes, I agree, though in practice I'm unsure how you would approach it as you can't just remove the prefix.

[cakebaker]

@BenWiederhake Thanks!

[BenWiederhake]

you can't just remove the prefix

I was about to create a new PR removing the prefix everywhere. So let me ask the blunt, but honest question: What is the disadvantage?

[cakebaker]

The "disadvantage" is that you often have to adapt the new function name because something like directory (an example from test_cat.rs) is a bad function name. And with the number of tests we have it's a lot of work.