`m.request` should support more data for the request body

[pygy]

Per https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/send

A body of data to be sent in the XHR request. This can be:

• A Document, in which case it is serialized before being sent.
• An XMLHttpRequestBodyInit, which per the Fetch spec can be a Blob, an ArrayBuffer, a TypedArray, a DataView, a FormData, a URLSearchParams, or a string object or value.
• null

We only support a subset of these:

mithril.js/request/request.js

Lines 143 to 146 in 645cf66

	if (body == null) xhr.send()
	else if (typeof args.serialize === "function") xhr.send(args.serialize(body))
	else if (body instanceof $window.FormData || body instanceof $window.URLSearchParams) xhr.send(body)
	else xhr.send(JSON.stringify(body))

Mithril.js version:
All versions up to 2.2.2

[plybrd]

Uploading with the PUT method to a webDAV server needs:
|| body instanceof $window.Blob

See TAF a WebDAV client in JavaScript (just 10KB) featuring mithril.js

[pygy]

@plybrd do you feel like creating a PR for this against the v2.x branch? If so, it would be much appreciated.

The implementation is trivial, and as far as testing goes, I wouldn't worry about faking the functionality in detail. Adding stub constructors like we do for FormData in the xhr mocks will be enough:

mithril.js/test-utils/xhrMock.js

Lines 14 to 16 in e0996bd

	function FormData() {}
	var $window = {
	FormData: FormData,

The common prototype for all typed arrays can be accessed through Object.getPrototypeOf(&window.Int8Array). You can cache that value in reqest/request.js next to the PromiseProxy definition