Fix project leaking in tests

The project was leaking via MockApplication -> LowMemoryWatcherManager -> List<Project>
It happened due to unregistered disposable provided to the MockApplication

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinCoreEnvironment.kt

@@ -543,7 +543,14 @@ class KotlinCoreEnvironment private constructor(
         ): KotlinCoreApplicationEnvironment {
             synchronized(APPLICATION_LOCK) {
                 if (ourApplicationEnvironment == null) {
-                    val disposable = Disposer.newDisposable()
+                    val disposable = if (unitTestMode) {
+                        parentDisposable
+                    } else {
+                        // TODO this is a memory leak in the compiler, as this Disposable is not registered and thus is never disposed
+                        // but using parentDisposable as disposable in compiler, causes access to application extension points after
+                        // they was disposed, this needs to be fixed
+                        Disposer.newDisposable("Disposable for the KotlinCoreApplicationEnvironment")
+                    }
                     ourApplicationEnvironment = createApplicationEnvironment(disposable, configuration, unitTestMode)
                     ourProjectCount = 0
                     Disposer.register(disposable, Disposable {

idea/idea-frontend-fir/idea-fir-low-level-api/tests/org/jetbrains/kotlin/idea/fir/low/level/api/test/base/AbstractLowLevelApiTest.kt

@@ -76,6 +76,7 @@ abstract class AbstractLowLevelApiTest : TestWithDisposable() {
     protected fun runTest(path: String) {
         testDataPath = Paths.get(path)
         val testConfiguration = testConfiguration(path, configure)
+        Disposer.register(disposable, testConfiguration.rootDisposable)
         val testServices = testConfiguration.testServices
         val moduleStructure = testConfiguration.moduleStructureExtractor.splitTestDataByModules(
             path,