Tabs: cleanup and improvements

[chad1008]

What?

A few small updates to the Tabs component family:

1. use useTabContext() consistently, instead of sometimes using useContext()
2. memoize the context value
3. expose Tabs.Context
4. add sub-components to Storybook

Why?

These are items that came up while working on other things. While they could be broken into their own separate PRs, they felt small enough to batch together. More specifically:

useTabContext()
No change in behavior here, it just wasn't being used consistently

Memoize context value
Was causing unnecessary re-renders.

Expose Tabs.Context
In some implications involving slot/fills, it's necessary to wrap subcomponents in an additional context provider. See #55360 for a real-life example. This also meant updating the warning thrown when context is missing to include the possibility of using a Tabs.Context.Provider

Add sub-components to Storybook
I forgot them initially, but now they can be viewed in the component docs in Storybook.

Testing Instructions

N/A, other than making sure all the tests pass.

[github-actions]

Flaky tests detected in 34ae69d.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/6897370662
📝 Reported issues:

• [Flaky Test] should partially select with shift + click (@webkit) #53524 in /test/e2e/specs/editor/various/multi-block-selection.spec.js

[ciampo]

LGTM 🚀

Good to be merged once comments are addressed