Move getting source position to manager thread in tests

Real usages are performed in this thread too. Using AWT now fails
under runInReadActionWithWriteActionPriorityWithRetries added in
https://github.com/JetBrains/intellij-community/commit/b0e995b41e9f4c0d7a64b912d3708da179cf413c

idea/tests/org/jetbrains/kotlin/idea/debugger/evaluate/AbstractKotlinEvaluateExpressionTest.kt

@@ -210,7 +210,7 @@ abstract class AbstractKotlinEvaluateExpressionTest : KotlinDebuggerTestBase() {
     }
 
     private fun SuspendContextImpl.printFrame(variablesView: XVariablesView, watchesView: XWatchesViewImpl, config: PrinterConfig) {
-        val tree = variablesView.tree!!
+        val tree = variablesView.tree
         expandAll(
                 tree,
                 {
@@ -316,7 +316,9 @@ abstract class AbstractKotlinEvaluateExpressionTest : KotlinDebuggerTestBase() {
                 append(getPrefix(descriptor))
                 append(label)
                 if (config.shouldRenderSourcesPosition() && hasSourcePosition(descriptor)) {
-                    val sp = SourcePositionProvider.getSourcePosition(descriptor, myProject, debuggerContext)
+                    val sp = invokeInManagerThread {
+                        SourcePositionProvider.getSourcePosition(descriptor, myProject, debuggerContext)
+                    }
                     append(" (sp = ${render(sp)})")
                 }