ScriptDependenciesLoader: Fix freeze on notifyRootsChanged

In 4f3f4dd, launch(EDT(project)) was replaced with TransactionGuard.submitTransaction to fix write in write-unsafe context.
Unfortunately submitTransaction will call action immediately if we are already on EDT. This causes IDE freeze.
By replacing submitTransaction with submitTransactionLater we are postponing work to the end of events queue (as it was before 4f3f4dd).
Also in isUnitTestMode we need to call action immediately as it was before 4f3f4dd.

#KT-25958 Fixed

idea/idea-core/src/org/jetbrains/kotlin/idea/core/script/dependencies/ScriptDependenciesLoader.kt

@@ -109,13 +109,19 @@ abstract class ScriptDependenciesLoader(
     protected fun notifyRootsChanged() {
         if (!shouldNotifyRootsChanged) return
 
-        TransactionGuard.submitTransaction(project, Runnable {
+        val doNotifyRootsChanged = Runnable {
             runWriteAction {
                 if (project.isDisposed) return@runWriteAction
 
                 ProjectRootManagerEx.getInstanceEx(project)?.makeRootsChange(EmptyRunnable.getInstance(), false, true)
                 ScriptDependenciesModificationTracker.getInstance(project).incModificationCount()
             }
-        })
+        }
+
+        if (ApplicationManager.getApplication().isUnitTestMode) {
+            doNotifyRootsChanged.run()
+        } else {
+            TransactionGuard.getInstance().submitTransactionLater(project, doNotifyRootsChanged)
+        }
     }
 }