Fix bug: ClassDeclaration not guaranteed to be first declaration of a class (#22983)

* Fix bug: ClassDeclaration not guaranteed to be first declaration of a class

* fix test

tests/cases/fourslash/codeFixAddMissingMember_classIsNotFirstDeclaration.ts

@@ -0,0 +1,17 @@
+/// <reference path='fourslash.ts' />
+
+////interface C {}
+////class C {
+////}
+////new C().x = 0;
+
+verify.codeFix({
+    description: "Declare property 'x'",
+    index: 0,
+    newFileContent:
+`interface C {}
+class C {
+    x: number;
+}
+new C().x = 0;`,
+});