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/ContainingPackageLookupValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
index 0383534..f47c5e0 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
@@ -14,7 +14,7 @@
 package com.google.devtools.build.lib.skyframe;
 
 import com.google.common.base.Preconditions;
-import com.google.devtools.build.lib.packages.PackageIdentifier;
+import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.skyframe.SkyKey;
 import com.google.devtools.build.skyframe.SkyValue;