Introduce LT file abstraction in tests parallel to KtFile

allows to create a valid LT-based file with synthetic path important
for dumps comparisons in tests

compiler/test-infrastructure/tests/org/jetbrains/kotlin/test/services/SourceFileProvider.kt

@@ -6,6 +6,8 @@
 package org.jetbrains.kotlin.test.services
 
 import com.intellij.openapi.project.Project
+import org.jetbrains.kotlin.fir.lightTree.LightTree2Fir
+import org.jetbrains.kotlin.fir.lightTree.LightTreeFile
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.test.model.TestFile
 import org.jetbrains.kotlin.test.util.KtTestUtil
@@ -97,6 +99,20 @@ fun SourceFileProvider.getKtFilesForSourceFiles(testFiles: Collection<TestFile>,
     }.toMap()
 }
 
+fun SourceFileProvider.getLightTreeKtFileForSourceFile(testFile: TestFile): LightTreeFile {
+    val shortName = testFile.name.substringAfterLast('/').substringAfterLast('\\')
+    val file = getRealFileForSourceFile(testFile)
+    val lightTree = LightTree2Fir.buildLightTree(file.readText())
+    return LightTreeFile(lightTree, shortName, "/$shortName") // emulating behavior of KtTestUtil.createFile so path looks the same in testdata
+}
+
+fun SourceFileProvider.getLightTreeFilesForSourceFiles(testFiles: Collection<TestFile>): Map<TestFile, LightTreeFile> {
+    return testFiles.mapNotNull {
+        if (!it.isKtFile) return@mapNotNull null
+        it to getLightTreeKtFileForSourceFile(it)
+    }.toMap()
+}
+
 val TestFile.isKtFile: Boolean
     get() = name.endsWith(".kt") || name.endsWith(".kts")