Report error on circular local dependencies (#731)

If a stack overflow is found during project evaluation, present any
circular imports found in the dependency graph.

pkl-core/src/main/resources/org/pkl/core/errorMessages.properties

@@ -827,6 +827,21 @@ Microbenchmark is a constant expression.
 stackOverflow=\
 A stack overflow occurred.
 
+cannotHaveCircularProjectDependenciesSingle=\
+Local project dependencies cannot be circular.\n\
+\n\
+Cycle:\n\
+{0}
+
+cannotHaveCircularProjectDependenciesMultiple=\
+Local project dependencies cannot be circular.\n\
+\n\
+The following circular imports were found.\n\
+Not all of them are necessarily problematic.\n\
+The problematic cycles are those declared as local dependencies.\n\
+\n\
+{0}
+
 multipleUnionDefaults=\
 A type union cannot have more than one default type.