Use reference check first for minor throughput gain (#10138)

In microbenchmarks, this shows a 1-1.5% improvement on finding entries (which also impacts map creation).

The gain will increase for maps with larger collisions chain

Author: dougqh

internal-api/src/main/java/datadog/trace/api/TagMap.java

@@ -290,7 +290,7 @@ public final String tag() {
     }
 
     public final boolean matches(String tag) {
-      return this.tag.equals(tag);
+      return (this.tag == tag) || this.tag.equals(tag);
     }
 
     public abstract boolean isRemoval();