Lazy initialisation of LinkedList in TokenOperations constructor -> 7% performance gain for formatter

[bergmeister]

PR Summary

This is a simple optimizaton as many consumers that construct the TokenOperations class do not call APIs that use the LinkedList. This changes the CPU consumption of this class constructor during a format run from 8% to 1%. Of course one could optimize further but I suggest to do the quick wins first with little risk of code regression.
Performance gains are mainly in formatter rules but also in relatively expensive UseSupportsShouldProcess rule.

Also remove unused method. Technically this is a breaking change due to them being publicly exposed but I don't think people use them, the only usage that I can imagine is in custom rules. I did a global GitHub search and it confirmed that no one is probably using those APIs.

This class is quite disgusting overall, littered with TODOs and private/public methods spread across the file. Idea is to keep changes minimal and safe.

PR Checklist

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[rjmholt]

Awesome!

[rjmholt]

Also, is there a good reason to use a linked list here? Surely it should just be a List<>?

[bergmeister]

Also, is there a good reason to use a linked list here? Surely it should just be a List<>?

When you look at the callers, they use the .Previous and .Next properties of a LL, which makes the code easier to read I have to say. With this we reduced the overhead from 8% to 1% so although one could optimize more, this was an easy way of achieving much without having to change to much in the spirit of the 80-20 rule. Only once other, bigger perf impacts have been optimized, I'd come back to optimize the LinkedList away completely as well or at least create it only once and then share it.