Summary: Don't emit KeywordLookup thunks and machinery for namespaced keyword access
Description: When the compiler sees a keyword at the beginning of a sexpr, (:foo x), it emits some machinery that takes into account that 'x' could be a defrecord with a defined 'foo' field. This exists to fast-path it into a field lookup. Here is the supporting code from the target defrecord: https://github.com/clojure/clojure/blob/master/src/clj/clojure/core_deftype.clj#L185-L198
The compiler currently emits the same machinery for (:foo/bar x), a namespaced keyword access, but defrecords don't have any fast path field access for that. This trivial patch turns that scenario into a normal invocation.
Here is the disassembly for (fn [x] (:foo/bar x))
There are two static fields on the IFn also for every kw access.
With the trivial patch, it turns into a normal invoke. (emit the fn aka the namespaced keyword, then the args Aka the target, and call IFn invoke: kw.invoke(target))