[New] create ignorePrivate option for no-multi-comp rule

[vwillyams]

Adds a new option to no-multi-comp which ignores components that are not exported.

Currently WIP:

• Thorough testing, find edge cases. npm test wasn't working locally so I'm hoping to rely on CI for this.
• Comparisons between exports and React components probably needs more work. Maybe there's a pre-existing lib function for this. Maybe this functionality should be moved into lib.

[vwillyams]

FYI I will hopefully find time to have this ready for merge in the next 2-3 days. I'm going to get this working with RSCs and I also want to look at making the tests programmatically generated so that we can iterate over every possible permutation without having to write them all out individually (and risk missing something). In practice there's likely to be diminishing returns on that kind of testing but I assume that individual test cases are very cheap here and I don't really like the maintenance burden of the test cases I've added in this PR.

[vwillyams]

FYI I'm currently iterating on the test coverage and making sure this works in all cases. I didn't entirely expect the amount of complexity that would go into this feature! But it's been a fun learning process.