[FIR] make FirPropertyAccessor#propertySymbol non-nullable

we need it to restore property accessor by property

^KT-54311

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/declarations/FirPropertyAccessor.kt

@@ -42,7 +42,7 @@ abstract class FirPropertyAccessor : FirFunction(), FirContractDescriptionOwner,
     abstract override val body: FirBlock?
     abstract override val contractDescription: FirContractDescription
     abstract override val symbol: FirPropertyAccessorSymbol
-    abstract val propertySymbol: FirPropertySymbol?
+    abstract val propertySymbol: FirPropertySymbol
     abstract val isGetter: Boolean
     abstract val isSetter: Boolean
     abstract override val annotations: List<FirAnnotation>

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/declarations/builder/FirPropertyAccessorBuilder.kt

@@ -60,7 +60,7 @@ class FirPropertyAccessorBuilder : FirFunctionBuilder, FirAnnotationContainerBui
     override var body: FirBlock? = null
     var contractDescription: FirContractDescription = FirEmptyContractDescription
     lateinit var symbol: FirPropertyAccessorSymbol
-    var propertySymbol: FirPropertySymbol? = null
+    lateinit var propertySymbol: FirPropertySymbol
     var isGetter: Boolean by kotlin.properties.Delegates.notNull<Boolean>()
     override val annotations: MutableList<FirAnnotation> = mutableListOf()
     val typeParameters: MutableList<FirTypeParameter> = mutableListOf()

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/declarations/impl/FirPropertyAccessorImpl.kt

@@ -53,7 +53,7 @@ open class FirPropertyAccessorImpl @FirImplementationDetail constructor(
     override var body: FirBlock?,
     override var contractDescription: FirContractDescription,
     override val symbol: FirPropertyAccessorSymbol,
-    override val propertySymbol: FirPropertySymbol?,
+    override val propertySymbol: FirPropertySymbol,
     override val isGetter: Boolean,
     override val annotations: MutableList<FirAnnotation>,
     override val typeParameters: MutableList<FirTypeParameter>,