Prepare CLI reporting infrastructure for non-PSI diagnostics

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/messages/CompilerMessageLocation.kt

@@ -22,9 +22,11 @@ interface CompilerMessageSourceLocation : Serializable {
     val path: String
     val line: Int
     val column: Int
+    // NOTE: Seems that the end-of-location data do not belong here conceptually, and now causes confusion with other usages
+    // TODO: consider removing it and switching REPL/Scripting diagnostis to the higher-level entities (KtDiagnostics)
     val lineEnd: Int get() = -1
     val columnEnd: Int get() = -1
-    val lineContent: String?
+    val lineContent: String? // related to the (start) line/column only, used to show start position in the console output
 }
 
 data class CompilerMessageLocation private constructor(