Scripting: fix descriptor extraction, restore main-kts testing

Temporary solution for K1 - see comments in the code
it seems that a scenario reproduced in the MainKtsTest.testKt48812
wasn't covered with analogous changes before.
And it wasn't detected while main-kts tests weren't a part of the
K1 scripting tests.
The test is fixed now, and testing of main-kts is restored.

build.gradle.kts

@@ -708,6 +708,7 @@ tasks {
         dependsOn(":kotlin-scripting-jsr223-test:embeddableTest")
         dependsOn(":kotlin-scripting-ide-services-test:test")
         dependsOn(":kotlin-scripting-ide-services-test:embeddableTest")
+        dependsOn(":kotlin-main-kts-test:test")
     }
 
     register("scriptingK2Test") {