Allow nested sheets without boilerplate

[mozzius]

Due to the strict necessity of iOS native sheets needing to be nested, we were creating new portal groups manually and then prop drilling to the sub-dialogs. This felt like a leaky abstraction, so this PR handles this automatically ✨

This has let me delete all of the unnecessary prop drilling in more cases. I've kept the prop around for the more general-purpose components for if we want to use it in future, but they're no longer used

How it works

1. Dialogs get the Portal they use from context. the default value of the context is same as before (thus no top-level provider needed) (also can be overridden by prop still)
2. Dialogs set a new default portal provider for their children via <DefaultPortalOverride>

Test plan

1. Test normal dialogs work as before
2. Test nested dialogs work: within composer, prompt in muted words, "dialog with menu in it" in the storybook
3. Make sure it roughly works the same on web - I opted not to override the default portal for dialog content there

[github-actions]

Old size	New size	Diff
7.89 MB	7.89 MB	3.6 KB (0.04%)

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[estrattonbailey]

Do we still need this?

[mozzius]

Hailey seemed to want to keep it around, I'd be fine to rm personally

[haileyok]

Oh yea this is fine to RM now 👍

[estrattonbailey]

Is "default" the right word here? I feel like we could just call it PortalContext. The default is DefaultPortal, which is aptly named in this file. But this context overrides, and in the spirit of "not thinking about it", I think usePortal or like useParentPortal might make more sense? No strong feelings, just spitballing.

[mozzius]

useDefaultPortal makes sense in the context of it maybe being passed in via prop instead. you shouldn't need to know that the default portal might get overridden if in a sheet

[estrattonbailey]

LGTM

[haileyok]

Thank you for all the feedback on this 🙏