Fast-path Label#equals by first comparing the interned PackageIdentifier.

PiperOrigin-RevId: 199007753
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
index d8bf3bf..8d7ad19 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
@@ -46,6 +46,7 @@
 
   @AutoCodec.Instantiator
   public static PackageIdentifier create(RepositoryName repository, PathFragment pkgName) {
+    // Note: We rely on these being interned to fast-path Label#equals.
     return INTERNER.intern(new PackageIdentifier(repository, pkgName));
   }