Introduce unspecifiedJvmPlatform for clients without jvmTarget

Previously, a lot of clients used JvmPlatform as platform-marker,
without thinking about jvmTarget.

For the sake of migration, this commits introduced so-called
UnspecifiedJvmPlatform, which can be used for a time being, but
generally, all usages should be removed in  future.

compiler/tests-common/tests/org/jetbrains/kotlin/checkers/AbstractDiagnosticsTest.kt

@@ -594,7 +594,7 @@ abstract class AbstractDiagnosticsTest : BaseDiagnosticsTest() {
             when {
                 nameSuffix.isEmpty() -> null // TODO(dsavvinov): this leads to 'null'-platform in ModuleDescriptor
                 nameSuffix == "COMMON" -> CommonPlatforms.defaultCommonPlatform
-                nameSuffix == "JVM" -> JvmPlatforms.defaultJvmPlatform // TODO(dsavvinov): determine JvmTarget precisely
+                nameSuffix == "JVM" -> JvmPlatforms.unspecifiedJvmPlatform // TODO(dsavvinov): determine JvmTarget precisely
                 nameSuffix == "JS" -> JsPlatforms.defaultJsPlatform
                 nameSuffix == "NATIVE" -> KonanPlatforms.defaultKonanPlatform
                 else -> throw IllegalStateException("Can't determine platform by name $nameSuffix")

compiler/tests-common/tests/org/jetbrains/kotlin/fir/FirTestModuleInfo.kt

@@ -15,7 +15,7 @@ import org.jetbrains.kotlin.resolve.jvm.platform.JvmPlatformAnalyzerServices
 class FirTestModuleInfo(
     override val name: Name = Name.identifier("TestModule"),
     val dependencies: MutableList<ModuleInfo> = mutableListOf(),
-    override val platform: TargetPlatform = JvmPlatforms.defaultJvmPlatform,
+    override val platform: TargetPlatform = JvmPlatforms.unspecifiedJvmPlatform,
     override val analyzerServices: PlatformDependentAnalyzerServices = JvmPlatformAnalyzerServices
 ) : ModuleInfo {
     override fun dependencies(): List<ModuleInfo> = dependencies

compiler/tests-common/tests/org/jetbrains/kotlin/resolve/lazy/lazyResolveTestUtils.kt

@@ -67,7 +67,7 @@ private class TestModule(val dependsOnBuiltIns: Boolean) : ModuleInfo {
                 ModuleInfo.DependencyOnBuiltIns.NONE
 
     override val platform: TargetPlatform
-        get() = JvmPlatforms.defaultJvmPlatform
+        get() = JvmPlatforms.unspecifiedJvmPlatform
 
     override val analyzerServices: PlatformDependentAnalyzerServices
         get() = JvmPlatformAnalyzerServices