Remove `form-data` and `cross-fetch` dependencies

[aeharding]

FormData and fetch() are now supported in all modern/supported browsers and Node versions.

The last version of Node to not support these APIs was v16, which is EOL as of September 11th, 2023.

fetch():

• https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API#browser_compatibility
• https://caniuse.com/fetch

FormData:

• https://developer.mozilla.org/en-US/docs/Web/API/FormData#browser_compatibility
• https://caniuse.com/mdn-api_formdata

These dependencies add additional unnecessary bundle size for users. Therefore, I propose removing these dependencies and using the native implementations directly.

If support is still needed, they can be easily polyfilled by the consumer.