Avoid computing AST for IdentifierChecker

Basically, it's unnecessary to check anything when analysing stubs,
but it's complicated now to avoid that, so we just postpone
computing AST until reporting happens

compiler/frontend/src/org/jetbrains/kotlin/resolve/IdentifierChecker.kt

@@ -16,16 +16,16 @@
 
 package org.jetbrains.kotlin.resolve
 
-import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.diagnostics.DiagnosticSink
 import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.psi.KtSimpleNameExpression
 
 interface IdentifierChecker {
-    fun checkIdentifier(identifier: PsiElement?, diagnosticHolder: DiagnosticSink)
+    fun checkIdentifier(simpleNameExpression: KtSimpleNameExpression, diagnosticHolder: DiagnosticSink)
     fun checkDeclaration(declaration: KtDeclaration, diagnosticHolder: DiagnosticSink)
 
     object Default : IdentifierChecker {
-        override fun checkIdentifier(identifier: PsiElement?, diagnosticHolder: DiagnosticSink) {}
+        override fun checkIdentifier(simpleNameExpression: KtSimpleNameExpression, diagnosticHolder: DiagnosticSink) {}
         override fun checkDeclaration(declaration: KtDeclaration, diagnosticHolder: DiagnosticSink) {}
     }
 }

compiler/frontend/src/org/jetbrains/kotlin/resolve/LazyTopDownAnalyzer.kt

@@ -102,7 +102,7 @@ class LazyTopDownAnalyzer(
                 }
 
                 override fun visitPackageDirective(directive: KtPackageDirective) {
-                    directive.packageNames.forEach { identifierChecker.checkIdentifier(it.getIdentifier(), trace) }
+                    directive.packageNames.forEach { identifierChecker.checkIdentifier(it, trace) }
                     qualifiedExpressionResolver.resolvePackageHeader(directive, moduleDescriptor, trace)
                 }