[JVM IR] Move SYNTHETIC_ACCESSOR origin to IrDeclarationOrigin.Companion

We want to generate synthetic accessors not only on JVM (KT-64865),
so this is one of the prerequisites.

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclarationOrigin.kt

@@ -95,6 +95,12 @@ interface IrDeclarationOrigin {
         val LOWERED_SUSPEND_FUNCTION by IrDeclarationOriginImpl.Synthetic
 
         val SHARED_VARIABLE_IN_EVALUATOR_FRAGMENT by IrDeclarationOriginImpl.Synthetic
+
+        /**
+         * Used on synthetic accessor functions generated in place of references to e.g. private symbols in non-private inline functions,
+         * or `super` calls from lambdas and inline functions.
+         */
+        val SYNTHETIC_ACCESSOR by IrDeclarationOriginImpl.Synthetic
     }
 
     /**