feat: add feature flags exploration

[joshblack]

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• [ ] Added/updated tests
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• [ ] Changes are SSR compatible
• [ ] Tested in Chrome
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🦋 Changeset detected

Latest commit: 154d575594d1b97608fb2dcd761f2849fb7ed639

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

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@primer/react	Minor

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size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	88 KB (0%)
packages/react/dist/browser.umd.js	88.25 KB (0%)

[joshblack]

Note from UI mob pairing: add support for providing a (sync) function to check if something is enabled

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[siddharthkp]

Great idea! Love to see it.

Short feedback on usage: I think we should make the first iteration a little simpler for ourselves. I'm a little hesitant to support nested scopes right off the bat because usage in gh/gh can quickly get really hard to debug. (I'm thinking inconsistencies between pages, untested combination of feature flags, single instances of a component used with feature flag or the opposite)

Ideally, I'd like to start with a broad boundary (adjacent to ThemeProvider) and once we have some experience with it (and related tooling), make it more advanced.

Note for future: It would be nice if we had a common ThemeProvider across gh/gh and it was called something like PrimerProvider / PrimerContainer / PrimerBoundary (with exceptions for charting etc.)

[joshblack]

@siddharthkp would love to do something like PrimerApp or some kind of "App-level" component like what you described 👍 it would make it simple to add in things as "defaults" to projects that use Primer as a result.

And happy to defer on nesting if that would be helpful 👍 I think the only thing that felt critical is that we want a set of "default" feature flags (in this case the global ones) and that this should be merged in with what is given at the FeatureFlags level. This seemed important because otherwise call sites to FeatureFlags need to manage all flags and their default value, even if it's unrelated to what is being authored.