Avoid allocating lambda in PercentileTimer.computeIfAbsent

PercentileTimer.computeIfAbsent would delegate to Utils.computeIfAbsent, which actually
eagerly calls get and then putIfAbsent if the timer is not in the underlying map. Just directly
do that to avoid needing to allocate a lambda in the case the timer is present.

spectator-api/src/main/java/com/netflix/spectator/api/histogram/PercentileTimer.java

@@ -72,8 +72,14 @@ public final class PercentileTimer implements Timer {
    * site.
    */
   private static PercentileTimer computeIfAbsent(Registry registry, Id id, long min, long max) {
-    Object timer = Utils.computeIfAbsent(
-        registry.state(), id, i -> new PercentileTimer(registry, id, min, max));
+    Object timer = registry.state().get(id);
+    if (timer == null) {
+      PercentileTimer newTimer = new PercentileTimer(registry, id, min, max);
+      timer = registry.state().putIfAbsent(id, newTimer);
+      if (timer == null) {
+        return newTimer;
+      }
+    }
     return (timer instanceof PercentileTimer)
         ? ((PercentileTimer) timer).withRange(min, max)
         : new PercentileTimer(registry, id, min, max);