Allow use_self at function level

[martinthomson]

Like #5053, the use_self lint cannot be denied or allowed at the function level.

playground

As it is sometimes necessary to suppress this (e.g., #3410), it would be very useful to be able to target a specific function.

[Xk0nSid]

I would like to work on this issue as my first contribution to the project.

[flip1995]

Great! You can take a look at #5063 for some inspiration. If you have any questions, feel free to ask here or open a WIP PR.

[tnielens]

@Xk0nSid are you working on this one? I'd like to take it on if you're not.