Add DashboardLayout component to @toolpad/core (old, PR has been split)

[apedroferreira]

Docs/demo: https://deploy-preview-3343--mui-toolpad-docs.netlify.app/toolpad/core/components/dashboard-layout/

(once we have a navigation adapter we can make the demo sidebar links work with local state to provide better examples)
(API docs generation to be added next in separate PR)

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Ready with component tests, supports branding with logo and name for header, and navigation with nested items in sidebar. Over time we can expand on this and add more features / improvements, of course.

Please check the types in packages/toolpad-core/src/AppProvider/AppProvider.tsx + component props (packages/toolpad-core/src/AppProvider/AppProvider.tsx and packages/toolpad-core/src/layout/DashboardLayout/DashboardLayout.tsx) for the chosen API.

For now, AppProvider can be imported as a named import from @toolpad/core/AppProvider and DashboardLayout the same way from @toolpad/core/DashboardLayout. They can also be imported directly from @toolpad/core along with some maybe useful types such as Branding and Navigation.

Made it so that pnpm dev can be run to build Toolpad core + watch changes, and then a new Next.js project in playground/toolpad-core-nextjs can be run to develop and see changes live. We can add other projects/frameworks to the playground folder later.

Added documentation page for the DashboardLayout component with demos. The demos can also be used for development but in some cases a real application is better, of course.

Also added simple contribution instructions for Toolpad Core.

[apedroferreira]

Submitting for review again, CI is finally fixed.

[oliviertassinari]

It feels like some of the changes in this PR could be extracted to another one that isn't about the DashboardLayout component so that other people can work in parallel on other building blocks. Also, so we aim to never have a single PR open worked on for more than one week, continuously shipping.

[Janpot]

We will move towards nx for orchestration over time

[Janpot]

It feels like some of the changes in this PR could be extracted to another one that isn't about the DashboardLayout component so that other people can work in parallel on other building blocks.

Agreed. We could make the goal of the PR to set up the bare minimum of the basic layout component and provider so that we can test/prove the project setup works. Perhaps we should strip the configuration options from these components and concentrate on nailing the project setup so we can get this trough?
We can then concentrate on API in follow up PR.

[apedroferreira]

It feels like some of the changes in this PR could be extracted to another one that isn't about the DashboardLayout component so that other people can work in parallel on other building blocks.

Agreed. We could make the goal of the PR to set up the bare minimum of the basic layout component and provider so that we can test/prove the project setup works. Perhaps we should strip the configuration options from these components and concentrate on nailing the project setup so we can get this trough? We can then concentrate on API in follow up PR.

The current state just evolved naturally from review feedback + improving the build to fix some bugs with the component itself. I can probably split project setup from the component at this point though, at least, will see what else I can split.