Class-name symbols self-evaluate; extends? matches host classes; ISO_INSTANT

A slash-free dotted symbol with a Capitalized final segment (java.util.Map,
clojure.lang.Named, java.time.Instant) now self-evaluates to its name string
instead of resolving to nil — jolt models a class as its name, so a library
can extend a protocol to, or instance?-check, a host class jolt has no shim
for. hc-resolve-global classifies these as :class; the analyzer emits a const.

extends? now matches when either the query or the registered tag is a dotted
suffix of the other, so (extends? P java.util.Collection) finds the impl
extend registered under the canonical short tag.

Add DateTimeFormatter/ISO_INSTANT (UTC, trailing Z).

These unblock loading clojure.data.json, which dispatches JSONWriter on
java.util.Map/Collection/CharSequence/Instant and defaults a formatter to
ISO_INSTANT.

jolt-core/jolt/analyzer.clj

@@ -516,6 +516,9 @@
                 ;; jolt.passes.numeric types a call to it (an accumulator over the result).
                 :var (cond-> (var-ref (:ns r) (:name r)) (:num-ret r) (assoc :num-ret (:num-ret r)))
                 :host (host-ref (:name r))
+                ;; a class-name symbol (java.util.Map) self-evaluates to its name
+                ;; string — jolt models a class as its name, with no JVM classes.
+                :class (const (:name r))
                 ;; :unresolved — emitting a var-ref here would auto-intern an
                 ;; UNBOUND var, so a typo'd symbol would die later as 'Cannot call
                 ;; nil as a function' with no hint which symbol.