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/tests-common/tests/org/jetbrains/kotlin/codegen/SMAPTestUtil.kt

@@ -25,6 +25,7 @@ import org.jetbrains.kotlin.codegen.inline.GENERATE_SMAP
 import org.jetbrains.kotlin.test.KotlinBaseTest
 import org.jetbrains.kotlin.test.util.JUnit4Assertions
 import org.junit.Assert
+import java.io.File
 import java.io.StringReader
 
 object SMAPTestUtil {
@@ -62,7 +63,7 @@ object SMAPTestUtil {
         }.associateBy { it.sourceFile }
 
         for (source in sourceData) {
-            val ktFileName = "/" + source.sourceFile
+            val ktFileName = "/" + File(source.sourceFile).name
                 .replace(".smap-nonseparate-compilation", ".kt")
                 .replace(".smap-separate-compilation", ".kt")
                 .replace(".smap", ".kt")