Support passing children as props to a React component

[HiDeoo]

Changes

This PR fixes #5493.

Passing children as props to a React component, e.g. <WithChildren client:load children="test" /> would break in production with the component disappearing after hydration and React complaining with the following error:

Hydration failed because the initial UI does not match what was rendered on the server.

When creating the static HTML element for children, the props.children props was previously ignored. This PR introduces a change to fallback to props.children if children is not defined which fixes the issue.

This PR also adds this change to packages/integrations/react/server-v17.js for the React 17 integration, altho, while adding this, I noticed that the changes introduced in #4756 were not applied to the React 17 integration so I added them as well.

Testing

I updated the react-component fixture for astro to include a new WithChildren component rendering the children props and updated the associated test to render this component twice, once with children and once with props.children and assert that the rendered HTML is the same (which would fail without the changes in this PR as the <astro-slot> was missing in the second case).

I also manually tested locally this change in a local repro using the file: pnpm protocol and confirmed a component using children passed down as props is now properly rendered in production and the React hydration error is gone.

Docs

I could not find any specific mention regarding this specific behavior in the docs and I'm not sure if it's worth mentioning it.

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[HiDeoo]

Not sure what is going on regarding the CI failure only on macOS as I cannot repro locally (even on macOS) and it looks like it is related to a timeout issue in a Astro CLI related test which should not be impacted by this pull request 😕

[Princesseuh]

Not sure what is going on regarding the CI failure only on macOS as I cannot repro locally (even on macOS) and it looks like it is related to a timeout issue in a Astro CLI related test which should not be impacted by this pull request 😕

The test is probably just flaky, no worries!

[natemoo-re]

This is a great fix, thank you!