Introduce clojure-ts-add-arity refactoring command

[rrudakov]

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[bbatsov]

I'm guessing you can extract some private function checking whether the form at point is function-like. I assume that would be useful for other things down the road.

[rrudakov]

I've done a small refactoring in this PR and extracted some helper functions, such as clojure-ts--search-list-form-at-point or clojure-ts--list-node-sym-text or clojure-ts--parent-until (which I wish was part of treesit.el). This particular regexp and the following query is very unlikely going to be used anywhere else, it's too specific. If I extracted it to a function I would have to give it a name that indicates that it returns a node that represents a construct to which an arity could be added. We can always extract it if we need it in other place.

[rrudakov]

Thanks for quick review!