Allow theme switcher override with slots

[apedroferreira]

Closes #4151 and #4291

• Include ThemeSwitcher component in toolbarActions slot so it can be hidden
• Export existing ThemeSwitcher and ToolbarActions (default slot) components
• Add example of popover menu & custom theme switcher in DashboardLayout demo page in docs

https://deploy-preview-4340--mui-toolpad-docs.netlify.app/toolpad/core/react-dashboard-layout/#customization

[bharatkashyap]

Looks good! The demo and explanation of the slots seems clear to me. Perhaps we can have a diagram eventually when we have more slots

[apedroferreira]

Looks good! The demo and explanation of the slots seems clear to me. Perhaps we can have a diagram eventually when we have more slots

Yeah, will kind of see how it evolves as we go, the new "Examples" section should help show some particular scenarios that might be useful.

[apedroferreira]

@bharatkashyap I just noticed this if you sign out in the "Account in sidebar" example:

Probably no need to fix it in this release, just ran into it! Also not sure how to best handle it in the mini variant of the sidebar...

[bharatkashyap]

Probably no need to fix it in this release, just ran into it! Also not sure how to best handle it in the mini variant of the sidebar...

Thanks for that catch! I'll open an issue to track this