[K/N][tests] Make mention of the test data file grouping more visible

When running `codegen/box` tests, Kotlin/Native test infrastructure
divides test data files into groups and compiles each group in a single
compilation.
As a result, compilation problem with one test can cause an unrelated
nearby test to fail.

To make this less frustrating, this commit adjusts test failure reports:
it moves the test grouping mention from the bottom of a report to the
top and makes the wording more clear and actionable.

native/native.tests/tests/org/jetbrains/kotlin/konan/test/blackbox/support/LoggedData.kt

@@ -53,12 +53,7 @@ internal abstract class LoggedData {
         }
     }
 
-    class CompilerParameters(
-        private val home: KotlinNativeHome,
-        private val compilerArgs: Array<String>,
-        private val sourceModules: Collection<TestModule>,
-        private val environment: JVMEnvironment = JVMEnvironment() // Capture environment.
-    ) : LoggedData() {
+    class CompilerInput(private val sourceModules: Collection<TestModule>) : LoggedData() {
         private val testDataFiles: List<File>
             get() = buildList {
                 sourceModules.forEach { module ->
@@ -68,16 +63,30 @@ internal abstract class LoggedData {
                 sort()
             }
 
+        override fun computeText(): String = buildString {
+            val files = testDataFiles
+            if (files.size > 1) {
+                appendLine("NOTE: this compilation includes multiple test data files!")
+                appendLine(" So a test failure doesn't imply that something is wrong with that particular test.")
+                appendLine(" To check the single test data file, rerun the test with the following Gradle flag:")
+                appendLine("   -Pkotlin.internal.native.test.forceStandalone=true")
+                appendLine()
+                appendList("TEST DATA FILES (COMPILED TOGETHER):", testDataFiles)
+            } else {
+                appendLine("TEST DATA FILE: ${files.singleOrNull()}")
+            }
+        }
+    }
+
+    class CompilerParameters(
+        private val home: KotlinNativeHome,
+        private val compilerArgs: Array<String>,
+        private val environment: JVMEnvironment = JVMEnvironment() // Capture environment.
+    ) : LoggedData() {
         override fun computeText() = buildString {
             appendArguments("COMPILER ARGUMENTS:", listOf(home.dir.resolve("bin/kotlinc-native").path) + compilerArgs)
             appendLine()
             appendLine(environment)
-
-            val testDataFiles = testDataFiles
-            if (testDataFiles.isNotEmpty()) {
-                appendLine()
-                appendList("TEST DATA FILES (COMPILED TOGETHER):", testDataFiles)
-            }
         }
     }
 
@@ -100,6 +109,7 @@ internal abstract class LoggedData {
 
     class CompilationToolCall(
         private val toolName: String,
+        private val input: LoggedData?,
         private val parameters: LoggedData,
         val exitCode: ExitCode,
         val toolOutput: String,
@@ -113,6 +123,8 @@ internal abstract class LoggedData {
             )
 
             return buildString {
+                input?.let(::appendLine)
+
                 if (problems.isNotEmpty()) {
                     appendLine("$toolName PROBLEMS:")
                     problems.forEach(::appendLine)

native/native.tests/tests/org/jetbrains/kotlin/konan/test/blackbox/support/compilation/TestCompilation.kt

@@ -89,7 +89,8 @@ internal abstract class BasicCompilation<A : TestCompilationArtifact>(
             applySources()
         }
 
-        val loggedCompilerParameters = LoggedData.CompilerParameters(home, compilerArgs, sourceModules)
+        val loggedCompilerInput = LoggedData.CompilerInput(sourceModules)
+        val loggedCompilerParameters = LoggedData.CompilerParameters(home, compilerArgs)
 
         val (loggedCompilerCall: LoggedData, result: TestCompilationResult.ImmediateResult<out A>) = try {
             val compilerToolCallResult = when (compilerOutputInterceptor) {
@@ -105,8 +106,15 @@ internal abstract class BasicCompilation<A : TestCompilationArtifact>(
 
             val (exitCode, compilerOutput, compilerOutputHasErrors, duration) = compilerToolCallResult
 
-            val loggedCompilationToolCall =
-                LoggedData.CompilationToolCall("COMPILER", loggedCompilerParameters, exitCode, compilerOutput, compilerOutputHasErrors, duration)
+            val loggedCompilationToolCall = LoggedData.CompilationToolCall(
+                "COMPILER",
+                loggedCompilerInput,
+                loggedCompilerParameters,
+                exitCode,
+                compilerOutput,
+                compilerOutputHasErrors,
+                duration
+            )
 
             val result = if (exitCode != ExitCode.OK || compilerOutputHasErrors)
                 TestCompilationResult.CompilationToolFailure(loggedCompilationToolCall)
@@ -282,6 +290,7 @@ internal class CInteropCompilation(
 
             val loggedInteropCall = LoggedData.CompilationToolCall(
                 toolName = "CINTEROP",
+                input = null,
                 parameters = loggedCInteropParameters,
                 exitCode = exitCode,
                 toolOutput = cinteropOutput,