Optimize entry size when the singleton weigher is used

In this case the cache acts the same as maximumSize, but the caller
constructed using maximumWeight + weigher. The per-entry weight field
is not needed, so the maximumSize's entry should be used instead. This
allows optimizing when configured like in [1].

[1] https://gerrit-review.googlesource.com/c/gerrit/+/244612

caffeine/src/javaPoet/java/com/github/benmanes/caffeine/cache/NodeSelectorCode.java

@@ -81,7 +81,8 @@ private NodeSelectorCode maximum() {
     block
         .beginControlFlow("if (builder.evicts())")
             .addStatement("sb.append('M')")
-            .beginControlFlow("if ((isAsync && builder.evicts()) || builder.isWeighted())")
+            .beginControlFlow("if (isAsync "
+                + "|| (builder.isWeighted() && (builder.weigher != Weigher.singletonWeigher())))")
                 .addStatement("sb.append('W')")
             .nextControlFlow("else")
                 .addStatement("sb.append('S')")