fix: support fields with hyphenated API IDs

[seanlail]

Closes https://github.com/prismicio/prismic-ts-codegen/issues/6

Types of changes

• [ ] Chore (a non-breaking change which is related to package maintenance)
• [x] Bug fix (a non-breaking change which fixes an issue)
• [ ] New feature (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Description

Codegen was failing if a field name included hyphens. This PR sets the value correctly using a template literal and wrapping in quotes.

Before	After
```typescript interface Example { my-field: string; } ```	```typescript interface Example { "my-field": string; } ```

Checklist:

• [ ] My change requires an update to the official documentation.
• [x] All TSDoc comments are up-to-date and new ones have been added where necessary.
• [x] All new and existing tests are passing.

[codecov-commenter]

Codecov Report

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[angeloashmore]

Thanks @seanlail, this looks great. I added a few more tests to check types with child fields, such as Group fields and Slices.