fix signatures for set!

[shaunlebron]

All of the following are equivalent, but the first is not documented:

• (set! obj -field val)
• (set! (. obj -field) val)
• (set! (.-field obj) val)

Also, the second one is documented wrong as:

(set! (.- instance-expr instanceFieldName-symbol) expr)
;        ^ space should be removed

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example using doto:

(def obj (doto (create-obj)
           (set! -field1 1)
           (set! -field2 2)))

the arity is only documented here in a parser comment:

(defmethod parse 'set!
  [_ env [_ target val alt :as form] _ _]
  (let [[target val] (if (= 4 (count form))
                       ;; (set! o -prop val)
                       [`(. ~target ~val) alt]

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source from slack:

https://clojurians.slack.com/archives/C03S1KBA2/p1704890400974659