[KT-63275] Add a nullable body property to SIR functions

native/swift/sir/tree-generator/src/org/jetbrains/kotlin/sir/tree/generator/SwiftIrTree.kt

@@ -84,6 +84,7 @@ object SwiftIrTree : AbstractSwiftIrTreeBuilder() {
         +field("name", string)
         +listField("parameters", parameterType)
         +field("returnType", typeType)
+        +field("body", functionBodyType, nullable = true, mutable = true)
     }
 
     val foreignFunction by element {

native/swift/sir/tree-generator/src/org/jetbrains/kotlin/sir/tree/generator/Types.kt

@@ -14,6 +14,7 @@ val originType = type(BASE_PACKAGE, "SirOrigin", TypeKind.Class)
 val parameterType = type(BASE_PACKAGE, "SirParameter", TypeKind.Class)
 val typeType = type(BASE_PACKAGE, "SirType", TypeKind.Class)
 val enumCaseType = type(BASE_PACKAGE, "SirEnumCase", TypeKind.Class)
+val functionBodyType = type(BASE_PACKAGE, "SirFunctionBody", TypeKind.Class)
 
 private const val VISITORS_PACKAGE = "$BASE_PACKAGE.visitors"