IrFunctionExpression: add 'origin'

This is actually either a LAMBDA or an ANONYMOUS_FUNCTION.
Not quite sure if it's really required, but some tools such as IR-based
decompiler might require this information.

compiler/testData/ir/irText/declarations/annotations/delegateFieldWithAnnotations.txt

@@ -22,7 +22,7 @@ FILE fqName:<root> fileName:/delegateFieldWithAnnotations.kt
       EXPRESSION_BODY
         CALL 'public final fun lazy <T> (initializer: kotlin.Function0<T of kotlin.lazy>): kotlin.Lazy<T of kotlin.lazy> declared in kotlin' type=kotlin.Lazy<kotlin.Int> origin=null
           <T>: kotlin.Int
-          initializer: FUN_EXPR type=kotlin.Function0<kotlin.Int>
+          initializer: FUN_EXPR type=kotlin.Function0<kotlin.Int> origin=LAMBDA
             FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> () returnType:kotlin.Int 
               BLOCK_BODY
                 RETURN type=kotlin.Nothing from='local final fun <anonymous> (): kotlin.Int declared in <root>.test1$delegate'