Add "format" rule category

[andy-hanson]

PR checklist

• Addresses an existing issue: Suggestion: New rule categories #2759 (half of it)
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Adds a new RuleType and switches many rules to it.
The "format" category is for rules which would be handled by a formatter; these are rules which control the way an AST is represented as text.
I'm on the fence about whether to include "curly" here. It seems like a format-only rule, but I think a formatter would preserve whether you used curly braces around a one-line statement.

[giladgray]

@andy-hanson please update this branch so we can review it, or close it if not relevant.

[andy-hanson]

Running git commit normally broke a bunch of stuff, had to redo with git commit --no-verify.

[JoshuaKGoldberg]

Running git commit normally broke a bunch of stuff, had to redo with git commit --no-verify.

Should no longer be an issue for later updates after merging in from master now that #4214 and #4270 are in.

[adidahiya]

I will merge this but I would like to change the category name to "formatting", i'll do that in a separate PR