FIR LT: Introduce source file abstraction, carry it from parsing to IR

along with source lines mapping, allows to "emulate" usage of the
PSI files which allows to extract source file and line mapping info
on every stage from source element.
It makes sense to use this mapping for the error reporting too.

compiler/test-infrastructure-utils/tests/org/jetbrains/kotlin/sourceFiles/LightTreeFile.kt

@@ -0,0 +1,17 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.sourceFiles
+
+import com.intellij.lang.LighterASTNode
+import com.intellij.util.diff.FlyweightCapableTreeStructure
+import org.jetbrains.kotlin.KtSourceFile
+import org.jetbrains.kotlin.KtSourceFileLinesMapping
+
+data class LightTreeFile(
+    val lightTree: FlyweightCapableTreeStructure<LighterASTNode>,
+    val sourceFile: KtSourceFile,
+    val linesMapping: KtSourceFileLinesMapping
+)