[IR] Add isAssignable property to IrValueParameter.

Use it to check that only the value parameters that are explicitly
marked assignable are assigned.

Currently, the only parameters marked assignable are those for
default argument stubs.

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrFactoryImpl.kt

@@ -235,10 +235,11 @@ object IrFactoryImpl : IrFactory {
         varargElementType: IrType?,
         isCrossinline: Boolean,
         isNoinline: Boolean,
-        isHidden: Boolean
+        isHidden: Boolean,
+        isAssignable: Boolean,
     ): IrValueParameter =
         IrValueParameterImpl(
-            startOffset, endOffset, origin, symbol, name, index, type, varargElementType, isCrossinline, isNoinline, isHidden
+            startOffset, endOffset, origin, symbol, name, index, type, varargElementType, isCrossinline, isNoinline, isHidden, isAssignable
         )
 
     override fun createExpressionBody(

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrValueParameterImpl.kt

@@ -39,7 +39,8 @@ class IrValueParameterImpl(
     override var varargElementType: IrType?,
     override val isCrossinline: Boolean,
     override val isNoinline: Boolean,
-    override val isHidden: Boolean = false
+    override val isHidden: Boolean = false,
+    override val isAssignable: Boolean = false
 ) : IrValueParameter() {
     @ObsoleteDescriptorBasedAPI
     override val descriptor: ParameterDescriptor