Move the check whether a repository name contains a slash to PackageIdentifier, where it actually belongs.

--
MOS_MIGRATED_REVID=106086272

src/main/java/com/google/devtools/build/lib/analysis/ConfiguredRuleClassProvider.java

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredRuleClassProvider.java b/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredRuleClassProvider.java
index 896f292..36d497f 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredRuleClassProvider.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/ConfiguredRuleClassProvider.java
@@ -257,7 +257,7 @@
       try {
         return Label.parseAbsolute(from);
       } catch (LabelSyntaxException e) {
-        throw new IllegalArgumentException(from);
+        throw new IllegalArgumentException(from, e);
       }
     }
   });