TypeScript Property Signature missing definite

In the type and builder of Property Signature, there is a missing definite modifier.
I need it to generate properties like:
```typescript
class A {
b!: string
}
```
See: https://github.com/babel/babel/pull/7159
For people struggling with this, my current hack workaround:
```typescript
export function definiteTSPropertySignature(
key: namedTypes.Identifier,
typeAnnotation: namedTypes.TSTypeAnnotation
): namedTypes.TSPropertySignature {
const code = `class A {
${recast.print(key).code}!${recast.print(typeAnnotation).code}
}`;
const ast = parse(code);
return ast.program.body[0].body.body[0];
}
```

Locate the TypeScript Property Signature type and builder definitions, then compare their shape with the expected `b!: string` example and Babel PR 7159. Verify that the definite modifier can be represented and that generated TypeScript includes it, using the relevant existing tests if available.

Written by the indexing model from the issue text.