[Symfony 5.2] Rename setProviderKey()/getProviderKey() to setFirewallName()/getFirewallName()

[simivar]

Part of #4824

[TomasVotruba]

Thank you

Feel free to send multiple PRs at the same time. It's almost always ready to merge so it would be easier to merge them at once :)

[simivar]

I mostly add them as soon as I have them ready to not get any conflicts. I will try to group them a little to open a few at once :)

[TomasVotruba]

Adding new rule is usually 100 % isolated from other each other.

In case of buch of rules for single set, I create 5 PRs with each one rule. Then 1 PR that edits the sets.

We merge very quickly, so conflicts usually apear only on PRs that are being worked on for weeks.