[Platform API] Introduce fundamental abstraction of Platform

This is a large commit, which introduces general API for working with
abstraction of Platform.

- Add new abstraction to 'core' - SimplePlatform - which represents
exactly one platform
  - Clients are strongly prohibited to create instances of SimplePlatform
  by hand, instead, corresponding *Platforms abstraction should be used
  (e.g. JvmPlatforms, JsPlatforms, KonanPlatforms)

- Move TargetPlatform to 'core', it represents now a collection of
SimplePlatforms
  - Clients are strongly encouraged to use TargetPlatform
    (not SimplePlatform) in API, to enforce checks for multiplatform

- Provide a helper-extensions to work with TargetPlatform
(in particular, for getting a specific component platform)

- Remove MultiTargetPlatform in favour of TargetPlatform
  - Notably, this commit leaves another widely used duplicated abstraction,
    namely, IdePlatform. For the sake sanity, removal of IdePlatform is
    extracted in the separate commit.

idea/idea-maven/src/org/jetbrains/kotlin/idea/maven/configuration/KotlinJavaMavenConfigurator.kt

@@ -26,8 +26,8 @@ import org.jetbrains.kotlin.idea.configuration.hasKotlinJvmRuntimeInScope
 import org.jetbrains.kotlin.idea.maven.PomFile
 import org.jetbrains.kotlin.idea.versions.getDefaultJvmTarget
 import org.jetbrains.kotlin.idea.versions.getStdlibArtifactId
-import org.jetbrains.kotlin.resolve.TargetPlatform
-import org.jetbrains.kotlin.resolve.jvm.platform.JvmPlatform
+import org.jetbrains.kotlin.platform.TargetPlatform
+import org.jetbrains.kotlin.platform.jvm.JvmPlatforms
 
 class KotlinJavaMavenConfigurator : KotlinMavenConfigurator(
     KotlinJavaMavenConfigurator.TEST_LIB_ID,
@@ -68,7 +68,7 @@ class KotlinJavaMavenConfigurator : KotlinMavenConfigurator(
     }
 
     override val targetPlatform: TargetPlatform
-        get() = JvmPlatform
+        get() = JvmPlatforms.defaultJvmPlatform
 
     companion object {
         private const val NAME = "maven"

idea/idea-maven/src/org/jetbrains/kotlin/idea/maven/configuration/KotlinJavascriptMavenConfigurator.kt

@@ -21,8 +21,8 @@ import org.jetbrains.idea.maven.dom.model.MavenDomPlugin
 import org.jetbrains.kotlin.idea.configuration.hasKotlinJsRuntimeInScope
 import org.jetbrains.kotlin.idea.maven.PomFile
 import org.jetbrains.kotlin.idea.versions.MAVEN_JS_STDLIB_ID
-import org.jetbrains.kotlin.js.resolve.JsPlatform
-import org.jetbrains.kotlin.resolve.TargetPlatform
+import org.jetbrains.kotlin.platform.TargetPlatform
+import org.jetbrains.kotlin.platform.js.JsPlatforms
 
 class KotlinJavascriptMavenConfigurator :
     KotlinMavenConfigurator(null, false, KotlinJavascriptMavenConfigurator.NAME, KotlinJavascriptMavenConfigurator.PRESENTABLE_TEXT) {
@@ -43,7 +43,7 @@ class KotlinJavascriptMavenConfigurator :
     }
 
     override val targetPlatform: TargetPlatform
-        get() = JsPlatform
+        get() = JsPlatforms.defaultJsPlatform
 
     override fun getMinimumSupportedVersion() = "1.1.0"
 

idea/idea-maven/test/org/jetbrains/kotlin/idea/maven/KotlinMavenImporterTest.kt

@@ -46,13 +46,13 @@ import org.jetbrains.kotlin.idea.framework.JSLibraryKind
 import org.jetbrains.kotlin.idea.framework.KotlinSdkType
 import org.jetbrains.kotlin.idea.project.languageVersionSettings
 import org.jetbrains.kotlin.idea.refactoring.toPsiFile
-import org.jetbrains.kotlin.js.resolve.JsPlatform
 import org.jetbrains.kotlin.platform.impl.*
 import org.jetbrains.kotlin.psi.KtFile
-import org.jetbrains.kotlin.resolve.TargetPlatform
-import org.jetbrains.kotlin.resolve.jvm.platform.JvmPlatform
 import org.jetbrains.kotlin.test.JUnit3RunnerWithInners
 import org.jetbrains.kotlin.test.JUnit3WithIdeaConfigurationRunner
+import org.jetbrains.kotlin.platform.TargetPlatform
+import org.jetbrains.kotlin.platform.js.JsPlatforms
+import org.jetbrains.kotlin.platform.jvm.JvmPlatforms
 import org.junit.Assert
 import org.junit.runner.RunWith
 import java.io.File
@@ -2970,8 +2970,8 @@ class KotlinMavenImporterTest : MavenImportingTestCase() {
 
         assertImporterStatePresent()
 
-        checkStableModuleName("project", "project", JvmPlatform, isProduction = true)
-        checkStableModuleName("project", "project", JvmPlatform, isProduction = false)
+        checkStableModuleName("project", "project", JvmPlatforms.defaultJvmPlatform, isProduction = true)
+        checkStableModuleName("project", "project", JvmPlatforms.defaultJvmPlatform, isProduction = false)
     }
 
     fun testStableModuleNameWhileUsngMaven_JS() {
@@ -3031,8 +3031,8 @@ class KotlinMavenImporterTest : MavenImportingTestCase() {
 
         // Note that we check name induced by '-output-file' -- may be it's not the best
         // decision, but we don't have a better one
-        checkStableModuleName("project", "test", JsPlatform, isProduction = true)
-        checkStableModuleName("project", "test", JsPlatform, isProduction = false)
+        checkStableModuleName("project", "test", JsPlatforms.defaultJsPlatform, isProduction = true)
+        checkStableModuleName("project", "test", JsPlatforms.defaultJsPlatform, isProduction = false)
     }
 
     private fun checkStableModuleName(projectName: String, expectedName: String, platform: TargetPlatform, isProduction: Boolean) {