Fixing onrenderhook chain

[dxlbnl]

Fixes: #263

I've renamed _root to _parent when nesting components. _renderHooks should be called when components are mounted, but it isn't being emptied. So adding _renderHooks to a component's parent should solve this issue.

_root is never being used anywhere else, and I don't think it should be needed?

[dxlbnl]

Hmm, so there's another usecase where there's no onrender on the containing element.

So there should be a parent-update chain.

[Rich-Harris]

Thanks for looking into this! Haven't had a chance to investigate yet myself, so the help is very much appreciated

[dxlbnl]

I've been looking into it a bit further, But I don't think I can make a decision.
The error (why the checks are failing) is due to that the root component is not mounted yet, when the onrender of ParentWidget -> Widget is being called.

I know of #40, but maybe onrender should be called oncreate. But then it shouldn't guarantee that it is mounted in the document. There could be a onmounted event, to handle stuff when it can be guaranteed to be mounted in the document.

So test onrender-fires-when-ready-nested could be counting on unspecified behaviour.

I'll also add my test case to the tests.

[Rich-Harris]

I've taken another run at this --> #273

[Rich-Harris]

Merged #273 so will close this — thanks again