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/frontend.java/src/org/jetbrains/kotlin/platform/jvm/JvmPlatform.kt

@@ -22,8 +22,13 @@ object JvmPlatforms {
     private val jvmTargetToJdkPlatform: Map<JvmTarget, TargetPlatform> =
         JvmTarget.values().map { it to JdkPlatform(it).toTargetPlatform() }.toMap()
 
-    val defaultJvmPlatform: TargetPlatform
-        get() = CompatJvmPlatform
+    // This platform is needed mostly for compatibility and migration of code base,
+    // as previously some clients used TargetPlatform just as platform-marker
+    // and didn't care about particular jvmTarget.
+    // TODO(dsavvinov): review all usages and choose proper JvmTarget
+    val unspecifiedJvmPlatform: TargetPlatform = CompatJvmPlatform
+
+    val defaultJvmPlatform: TargetPlatform = jvmTargetToJdkPlatform[JvmTarget.DEFAULT]!!
 
     val jvm16: TargetPlatform = jvmTargetToJdkPlatform[JvmTarget.JVM_1_6]!!
     val jvm18: TargetPlatform = jvmTargetToJdkPlatform[JvmTarget.JVM_1_8]!!
@@ -34,7 +39,7 @@ object JvmPlatforms {
     val allJvmPlatforms: List<TargetPlatform> = jvmTargetToJdkPlatform.values.toList()
 
     @Deprecated(
-        message = "Should be accessed only by compatibility layer, other clients should use 'defaultJvmPlatform'",
+        message = "Should be accessed only by compatibility layer, other clients should use 'unspecifiedJvmPlatform'",
         level = DeprecationLevel.ERROR
     )
     object CompatJvmPlatform : TargetPlatform(setOf(UNSPECIFIED_SIMPLE_JVM_PLATFORM)),

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/platform/JvmPlatform.kt

@@ -12,7 +12,7 @@ import org.jetbrains.kotlin.resolve.TargetPlatform
 
 @Deprecated(
     message = "This class is deprecated and will be removed soon, use API from 'org.jetbrains.kotlin.platform.*' packages instead",
-    replaceWith = ReplaceWith("JvmPlatforms.defaultJvmPlatform", "org.jetbrains.kotlin.platform.jvm.JvmPlatforms"),
+    replaceWith = ReplaceWith("JvmPlatforms.unspecifiedJvmPlatform", "org.jetbrains.kotlin.platform.jvm.JvmPlatforms"),
     level = DeprecationLevel.ERROR
 )
 interface JvmPlatform : TargetPlatform {