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).

host/chez/converters.ss

@@ -132,6 +132,8 @@
                          (jolt-symbol (substring a 0 i) (substring a (+ i 1) slen)))
                         (else (loop (- i 1))))))))
          ((keyword? a) (jolt-symbol (keyword-t-ns a) (keyword-t-name a)))
+         ;; (symbol a-var) -> the var's qualified symbol (clojure.spec.alpha/->sym).
+         ((var-cell? a) (jolt-symbol (var-cell-ns a) (var-cell-name a)))
          (else (error #f "symbol: requires string/symbol" a)))))
     ;; (symbol ns name): a nil namespace is the no-ns sentinel #f (NOT jolt-nil),
     ;; so (symbol nil "x") equals (symbol "x") and the reader literal 'x — jolt=