[FE] Preserve legacy contract description calls in bodies

^KT-55231 Fixed
^KTIJ-21012 Fixed

compiler/fir/analysis-tests/testData/resolveWithStdlib/delegates/annotationArgumentMapping.kt

@@ -8,6 +8,7 @@ class FirAnnotationArgumentMappingBuilder {
     }
 }
 
+@OptIn(ExperimentalContracts::class)
 fun buildAnnotationArgumentMapping(init: FirAnnotationArgumentMappingBuilder.() -> Unit): FirAnnotationArgumentMapping {
     contract {
         callsInPlace(init, InvocationKind.EXACTLY_ONCE)