Add stdlib-jdk7/8 to Kotlin IDEA plugin classpath

Motivation: standard library dynamically loads its JDK7/8 extensions by class name.
When these extensions are missing from the plugin classloader, they are loaded by
the parent classloader thus becoming assignment incompatible with the base class.

Fixes EA-120914

prepare/idea-plugin/build.gradle.kts

@@ -66,6 +66,8 @@ dependencies {
     packedJars(project(":core:builtins", configuration = "builtins"))
     sideJars(project(":kotlin-script-runtime"))
     sideJars(project(":kotlin-stdlib"))
+    sideJars(project(":kotlin-stdlib-jdk7"))
+    sideJars(project(":kotlin-stdlib-jdk8"))
     sideJars(project(":kotlin-reflect"))
     sideJars(project(":kotlin-compiler-client-embeddable"))
     sideJars(commonDep("io.javaslang", "javaslang"))