feat(web experiments): Emit web_experiment_applied event and do not render experiments for bots

[Phanatic]

Changes

1. Replace references to className with css which assigns the value of this field to the style attribute of an HTML element.
2. Introduce the ability to preview an Experiment variant in the browser without deploying the experiment.
3. Do not render web experiments if the viewer is a bot.
4. Emit the $web_experiment_applied event so we know if the visual changes actually got applied to a page.

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]

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Name	Status	Preview	Updated (UTC)
posthog-js	✅ Ready (Inspect)	Visit Preview	Oct 3, 2024 8:42am

[github-actions]

Size Change: +15.5 kB (+0.55%)

Total Size: 2.82 MB

Filename	Size	Change
dist/array.full.js	353 kB	+1.72 kB (+0.49%)
dist/array.full.no-external.js	352 kB	+1.72 kB (+0.49%)
dist/array.js	168 kB	+1.72 kB (+1.03%)
dist/array.no-external.js	167 kB	+1.72 kB (+1.04%)
dist/main.js	169 kB	+1.72 kB (+1.03%)
dist/module.full.js	353 kB	+1.72 kB (+0.49%)
dist/module.full.no-external.js	352 kB	+1.72 kB (+0.49%)
dist/module.js	168 kB	+1.72 kB (+1.03%)
dist/module.no-external.js	167 kB	+1.72 kB (+1.04%)

ℹ️ View Unchanged

Filename	Size
dist/all-external-dependencies.js	191 kB
dist/exception-autocapture.js	10.5 kB
dist/external-scripts-loader.js	2.35 kB
dist/recorder-v2.js	111 kB
dist/recorder.js	111 kB
dist/surveys-preview.js	59.8 kB
dist/surveys.js	66 kB
dist/tracing-headers.js	8.36 kB
dist/web-vitals.js	10.3 kB

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[dmarticus]

seems reasonable, easy to follow, nice tests – all good from me!

[dmarticus]

useful!

[jurajmajerik]

Sorry for not reviewing earlier, this is looking good!