Update ts codegen (#8421)

Makes the return type of `static getFullyQualifiedName()` be a string literal instead of just the string type

Update tests

Co-authored-by: Björn Harrtell <bjornharrtell@users.noreply.github.com>

tests/ts/my-game/example/struct-of-structs-of-structs.ts

@@ -20,7 +20,7 @@ a(obj?:StructOfStructs):StructOfStructs|null {
   return (obj || new StructOfStructs()).__init(this.bb_pos, this.bb!);
 }
 
-static getFullyQualifiedName():string {
+static getFullyQualifiedName(): "MyGame.Example.StructOfStructsOfStructs" {
   return 'MyGame.Example.StructOfStructsOfStructs';
 }