FIR IDE: use EntityWasGarbageCollectedException instead of ISE in ReadOnlyWeakRef

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/utils/EntityWasGarbageCollectedException.kt

@@ -5,6 +5,6 @@
 
 package org.jetbrains.kotlin.idea.frontend.api.fir.utils
 
-internal class EntityWasGarbageCollectedException(entity: String) : IllegalStateException() {
+class EntityWasGarbageCollectedException(entity: String) : IllegalStateException() {
     override val message: String = "$entity was garbage collected while KtAnalysisSession session is still valid"
 }

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/utils/ReadOnlyWeakRef.kt

@@ -18,7 +18,7 @@ constructor(value: V, val token: ValidityToken) {
     @Suppress("NOTHING_TO_INLINE")
     inline operator fun getValue(thisRef: Any, property: KProperty<*>): V =
         weakRef.get() ?: if (token.isValid()) {
-            error("Value of $property was garbage collected while analysis session is still valid")
+            throw EntityWasGarbageCollectedException(property.toString())
         } else {
             error("Accessing the invalid value of $property")
         }