replace 8 inline type assertions with named ast types

[cs01]

Summary

• Replace as { name: string; fieldType: string; tsType: string } with as ClassField in class.ts
• Replace as { name: string } on class fields with as ClassField in assignment-generator.ts, member.ts
• Replace as { name: string } on class arrays with as ClassNode in function-generator.ts, class.ts
• Replace as { name: string } on lifted functions with as LiftedFunction in arrow-functions.ts

Test plan

• npm run build passes
• npm run verify:quick passes (tests + stage 1 self-hosting)