Add the ability to get containing source file from SourceElement

compiler/frontend/src/org/jetbrains/kotlin/resolve/source/PsiSourceElement.kt

@@ -17,8 +17,17 @@
 package org.jetbrains.kotlin.resolve.source
 
 import com.intellij.psi.PsiElement
+import com.intellij.psi.PsiFile
 import org.jetbrains.kotlin.descriptors.SourceElement
+import org.jetbrains.kotlin.descriptors.SourceFile
 
 public interface PsiSourceElement : SourceElement {
     public val psi: PsiElement?
+
+    override fun getContainingFile(): SourceFile = psi?.containingFile?.let { PsiSourceFile(it) } ?: SourceFile.NO_SOURCE_FILE
+}
+
+public class PsiSourceFile(private val psiFile: PsiFile): SourceFile {
+    override fun equals(other: Any?): Boolean = other is PsiSourceFile && psiFile == other.psiFile
+    override fun hashCode(): Int = psiFile.hashCode()
 }