Allow custom `PageShell`, fix client router issue by passing `pageContext` on navigation

[acao]

As discussed. I think the hacks in the example I had to add are necessitated to the bug from bundling and singleton module mismatch with render/etc. Doesn't seem that the useContext() result from page context updates client side :/

I think this approach may cause a problem with the context client side? See useEffect/window.location hack for active state.

Todo:

• [x] custom PageShell and implementation in example
• [ ] docs
• [ ] add custom provider to example to demonstrate usage of custom PageShell such as react-intl

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 88152c97937a776b966fd082e217d90bcc36a29b

The changes in this PR will be included in the next version bump.

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| Name | Type | | ----- | ----- | | vilay | Patch |

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[XiNiHa]

I've fixed some bugs and tried to improve the overall design, tell me if you have any better ideas! Send me a review request after you're ready with the docs and example stuff :D

[acao]

great, thank you @XiNiHa ! i will finish this PR up then