feat: RemoteConfig loader

[benjackwhite]

Changes

Needs PostHog/posthog#26348

Work to implement the new RemoteConfig loader which will enable us to eventually replace /decide with /flags

This PR should not affect anything directly, but rather add a flagged _preview_remote_config option which will then load our new endpoint before calling decide (which we can then swap out for flags in the future).

The big change for reviewers is moving away from afterDecideResponse to onRemoteConfig which is almost the same as before. The things that require flags are changed to use the onFeatureFlags callbacks instead.

Checklist

• Tests for new code (see advice on the tests we use)
• Accounted for the impact of any changes across different browsers
• Accounted for backwards compatibility of any changes (no breaking changes in posthog-js!)

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated (UTC)
posthog-js	✅ Ready (Inspect)	Visit Preview	Dec 5, 2024 8:47am

[posthog-bot]

Hey @benjackwhite! 👋
This pull request seems to contain no description. Please add useful context, rationale, and/or any other information that will help make sense of this change now and in the distant Mars-based future.

[github-actions]

Size Change: +12.3 kB (+0.39%)

Total Size: 3.19 MB

Filename	Size	Change
dist/array.full.es5.js	259 kB	+1.28 kB (+0.5%)
dist/array.full.js	362 kB	+1.26 kB (+0.35%)
dist/array.full.no-external.js	361 kB	+1.19 kB (+0.33%)
dist/array.js	177 kB	+1.25 kB (+0.71%)
dist/array.no-external.js	175 kB	+1.17 kB (+0.67%)
dist/external-scripts-loader.js	2.36 kB	+71 B (+3.1%)
dist/main.js	177 kB	+1.25 kB (+0.71%)
dist/module.full.js	362 kB	+1.26 kB (+0.35%)
dist/module.full.no-external.js	361 kB	+1.19 kB (+0.33%)
dist/module.js	177 kB	+1.25 kB (+0.71%)
dist/module.no-external.js	175 kB	+1.17 kB (+0.67%)

ℹ️ View Unchanged

Filename	Size
dist/all-external-dependencies.js	206 kB
dist/customizations.full.js	12.5 kB
dist/dead-clicks-autocapture.js	14.3 kB
dist/exception-autocapture.js	9.37 kB
dist/recorder-v2.js	115 kB
dist/recorder.js	115 kB
dist/surveys-preview.js	57.6 kB
dist/surveys.js	63.2 kB
dist/tracing-headers.js	1.75 kB
dist/web-vitals.js	10.3 kB

_{compressed-size-action}

[pauldambra]

seems to work when hooked up with the parent PR though

so other than a though about error handling which might be fine 🚢