KT-9721:

- Kotlin/JS still uses package facades.
Handle them properly in StubClassBuilder parentStack.
- Generate backend-related diagnostics in IDE
using light class generation for file facades.
- Drop PackageFacadeStubCache.

idea/testData/checker/duplicateJvmSignature/functionAndProperty/topLevelMultifileRuntime.kt

@@ -0,0 +1,13 @@
+@file:JvmName("TopLevelMultifile")
+@file:JvmMultifileClass
+package test
+
+import kotlin.jvm.JvmName
+import kotlin.jvm.JvmMultifileClass
+
+<error descr="[CONFLICTING_JVM_DECLARATIONS] Platform declaration clash: The following declarations have the same JVM signature (getX()I):
+    fun <get-x>(): kotlin.Int
+    fun getX(): kotlin.Int">val x</error> = 1
+<error descr="[CONFLICTING_JVM_DECLARATIONS] Platform declaration clash: The following declarations have the same JVM signature (getX()I):
+    fun <get-x>(): kotlin.Int
+    fun getX(): kotlin.Int">fun getX()</error> = 1