Move PackageIdentifier to cmdline

This is necessary to have TargetResolver depend on it without making it depend
on the packages target. First step of #389.

--
MOS_MIGRATED_REVID=101790345
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
index 398f973..38b4ac4 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
@@ -22,6 +22,8 @@
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
 import com.google.devtools.build.lib.Constants;
+import com.google.devtools.build.lib.cmdline.PackageIdentifier;
+import com.google.devtools.build.lib.cmdline.PackageIdentifier.RepositoryName;
 import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.events.EventHandler;
 import com.google.devtools.build.lib.events.Location;
@@ -36,8 +38,6 @@
 import com.google.devtools.build.lib.packages.Package;
 import com.google.devtools.build.lib.packages.PackageFactory;
 import com.google.devtools.build.lib.packages.PackageFactory.Globber;
-import com.google.devtools.build.lib.packages.PackageIdentifier;
-import com.google.devtools.build.lib.packages.PackageIdentifier.RepositoryName;
 import com.google.devtools.build.lib.packages.Preprocessor;
 import com.google.devtools.build.lib.packages.RuleVisibility;
 import com.google.devtools.build.lib.packages.Target;