Allow access to parent before onBeforeMount() call

[kachurun]

Answer the following depending on the type of change you want to merge

Code

1. Have you added test(s) for your patch? If not, why not?
   Nothing to test

2. Can you provide an example of your patch in use?
   Demo (bug with 5.4.1):
   https://codesandbox.io/s/riotjs-5-provide-inject-bug-oub7z?file=/index.html
   Demo (no bug, patched 5.4.1)
   https://codesandbox.io/s/riotjs-5-provide-inject-k9m6u?file=/index.html

3. Is this a breaking change?
   No

Content

Provide a short description about what you have changed:

Hello. I tried to make behavior similar to vue setup and provide / inject (https://v3.vuejs.org/guide/composition-api-provide-inject.html#scenario-background). I need setup to be executed before any onBeforeMount until the component is rendered. In this case, I can in the setup inject the data provided in the parent component and for this I need to have access to the parent before the component is rendered. I noticed that the link to the parent is at the very beginning of the mount method of the components and I did not find any reason why it cannot be raised higher. In this case, what I want to do is working as expected.

[GianlucaGuarini]

I think that's a good Idea. Could you please add a small test for this patch? I think that's the right place for it https://github.com/riot/riot/blob/main/test/specs/lifecycle-events.spec.js

[kachurun]

@GianlucaGuarini Done

[GianlucaGuarini]

thank you