Parser: Do not produce qualified expressions without receiver in package directives. Add assertion on JetQualifiedExpression

#KT-6907 Fixed

compiler/testData/psi/packages/PackageSimpleNameLeadingDoubleDot.txt

@@ -0,0 +1,11 @@
+JetFile: PackageSimpleNameLeadingDoubleDot.kt
+  PACKAGE_DIRECTIVE
+    PsiElement(package)('package')
+    PsiWhiteSpace(' ')
+    PsiErrorElement:Package name must be a '.'-separated identifier list
+      PsiElement(DOT)('.')
+    PsiWhiteSpace(' ')
+    PsiErrorElement:Package name must be a '.'-separated identifier list
+      PsiElement(DOT)('.')
+    REFERENCE_EXPRESSION
+      PsiElement(IDENTIFIER)('a')