type: add other properties types to svelte transition functions

[leovoon]

Background

I'm trying to use another transition function as follows

<script lang='ts'>
  import { fly } from 'svelte/transition'

</script>

<Modal
  transitionWindow={fly}
  transitionWindowProps={{ y: 50, duration: 300 }} // Typescript is not happy
</Modal>

Currently Observed Behavior

The type is currently only supported for blurparam. This PR adds properties for fly, fade and slide functions and updates docs.

New Behavior

No typescript warnings

[flekschas]

Thanks for improving the type definitions! This looks good to me.

[flekschas]

New version with the improved type definition is out!