add support to return web API's File from handler

[kravetsone]

it('return web api\'s File', async () => {
		const app = new Elysia().get('/', () => new File(['Hello'], 'hello.txt', { type: 'text/plain' }))
		const res = await app.handle(req('/'))

		expect(res.headers.get('content-type')).toBe('text/plain;charset=utf-8')
		expect(await res.text()).toBe('Hello')
		expect(res.status).toBe(200)
		expect(res.headers.get('accept-ranges')).toBe('bytes')
		expect(res.headers.get('content-range')).toBe('bytes 0-4/5')
	})

[kravetsone]

Also

Maybe we should add https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Disposition or not?

[kravetsone]

• Approved

[kravetsone]