Remove `shouldYield()` from the `startTransitionEffect()` API

We need the runWithPriority() function from the scheduler package if we want to update state inside transition effect. This means that exposing shouldYield() doesn't solve scheduler dependency issue, so it's better to be consistent and always require direct usage of the scheduler package.

Wrap initial iteration with runWithPriority()

In order to have consistent priority context, we should wrap first iteration with runWithPriority() (next iterations uses scheduleCallback() which defines current priority)

Improve source-maps support

Add "src" to "files" in package.json so bundlers can pick-up source files for source-map generation.

Initial release

Release initial version of the useTransitionEffect() hook