[core] add simple TS types for variables and fields

[thepassle]

For fields and variables we can already add the 'simple' TS type by getting the: node.type.getText()

See: https://astexplorer.net/

Fixture:

class MyElement extends HTMLElement {
  foo: string = ''
}

customElements.define('my-element', MyElement);

Click on foo in the left panel of AST explorer, set compiler to typescript, and you'll see a type property in the PropertyDeclaration that you can call .getText() on

• [ ] Make sure the TS type overwrites any jsdoc types that a field or variable might have
• [ ] implement for fields
• [ ] implement for variables