spec.alpha: (symbol var), Compiler/demunge, MultiFn .dispatchFn/.getMethod, fn .applyTo

General fixes from clojure.spec.alpha's test suite.

- (symbol a-var) returns the var's qualified symbol (clojure.spec.alpha/->sym).
- clojure.lang.Compiler/demunge reverses Clojure's name munging
  ("clojure.core$odd_QMARK_" -> clojure.core/odd?); spec's fn-sym uses it.
- clojure.lang.MultiFn .dispatchFn / .getMethod — spec's multi-spec walks a
  multimethod through them.
- (.applyTo f args) applies a fn to a seq of args (spec instrument).

Most of spec.alpha's conform/explain/describe suite passes. Remaining gaps:
explain-data's :pred for a BARE fn predicate (jolt fns don't carry their defining
symbol, so fn-sym can't recover it), #inst form rendering, and instrument — follow-up.

make test green (+3 corpus rows, 0 new divergences), runtime only (no re-mint).

test/chez/corpus.edn

@@ -3386,4 +3386,7 @@
   {:suite "seq / take infinite count" :label "(take +Infinity coll) takes the whole coll" :expected "7" :actual "(count (take (/ 1.0 0.0) (range 7)))"}
   {:suite "host-interop / UUID + Long + shiftLeft" :label "(UUID. msb lsb), .shiftLeft, (Long. n)" :expected "[\"00000000-0000-007b-0000-0000000001c8\" 40 10 42]" :actual "[(str (java.util.UUID. 123 456)) (.shiftLeft 5 3) (.shiftRight 40 2) (Long. 42)]"}
   {:suite "host-interop / ThreadLocal proxy" :label "(proxy [ThreadLocal] [] (initialValue [] v)) get/set" :expected "[42 7]" :actual "(let [tl (proxy [ThreadLocal] [] (initialValue [] 42))] [(.get tl) (do (.set tl 7) (.get tl))])"}
+  {:suite "host-interop / symbol of a var" :label "(symbol var) returns its qualified symbol" :expected "clojure.core/inc" :actual "(symbol (var clojure.core/inc))"}
+  {:suite "host-interop / Compiler/demunge" :label "demunge reverses name munging" :expected "\"a/b?\"" :actual "(clojure.lang.Compiler/demunge \"a$b_QMARK_\")"}
+  {:suite "host-interop / MultiFn methods" :label ".getMethod / .dispatchFn on a multimethod" :expected "[true true true]" :actual "(do (defmulti mmc identity) (defmethod mmc :a [_] 1) [(some? (.getMethod mmc :a)) (nil? (.getMethod mmc :z)) (ifn? (.dispatchFn mmc))])"}
 ]