Add possibility to get line offsets from PsiIrFileEntry

This is needed for tests to be able to get offsets without explicit
file on disk.

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/PsiIrFileEntry.kt

@@ -53,6 +53,8 @@ class PsiIrFileEntry(val psiFile: PsiFile) : IrFileEntry {
 
     override fun toString(): String = getRecognizableName()
 
+    fun getLineOffsets() = lineStartOffsets.copyOf()
+
     fun findPsiElement(irElement: IrElement): PsiElement? {
         var psiElement = fileViewProvider.findElementAt(irElement.startOffset)
         while (psiElement != null) {

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/AdditionalIrUtils.kt

@@ -175,9 +175,10 @@ val File.lineStartOffsets: IntArray
         return buffer.toIntArray()
     }
 
-val IrFileEntry.lineStartOffsets
-    get() = File(name).let {
-        if (it.exists() && it.isFile) it.lineStartOffsets else IntArray(0)
+val IrFileEntry.lineStartOffsets: IntArray
+    get() = when (this) {
+        is PsiIrFileEntry -> this.getLineOffsets()
+        else -> File(name).let { if (it.exists() && it.isFile) it.lineStartOffsets else IntArray(0) }
     }
 
 class NaiveSourceBasedFileEntryImpl(