Build java9 modular artifacts under 'modular' classifier

Provide additional modular artifacts as a workaround for KT-21266

Update module-info declarations:
  - add new packages
  - add exports and opens for internal PlatformImplementations
  - remove exports of kotlin.coroutines.experimental.*

#KT-27919 Fixed

libraries/stdlib/jdk8/build.gradle

@@ -44,14 +44,25 @@ sourceSets {
 }
 
 jar {
-    manifestAttributes(manifest, project, 'Main', true)
+    manifestAttributes(manifest, project, 'Main' /*true*/)
     // TODO: enable as soon as this doesn't cause D8/DX to crash
     // from sourceSets.java9.output
 }
 
+task modularJar(type: Jar) {
+    dependsOn(jar)
+    manifestAttributes(manifest, project, 'Main', true)
+    classifier = 'modular'
+
+    from zipTree(jar.outputs.files.singleFile)
+    from sourceSets.java9.output
+}
+
+
 artifacts {
     archives sourcesJar
     archives javadocJar
+    archives modularJar
 }
 
 dist {