fix: improve ES6 bundling

[pauldambra]

#1525 - IE 11 tests are freezing in that PR and it's really hard to figure out why

have pulled many small changes out of that PR but the IE 11 tests still freeze

---

• improves detection/bundling of ES6 support for posthog-js by being more specific with the browser targets that are passed to the bundler
• adds a check that the array.full.js is ES6 compliant in CI

Does not update the browserslist value in package.json, since that is the change that appears to make CI freeze
I'd rather get the benefit of the ES6 compliant bundle in prod before fixing that

[vercel]

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Name	Status	Preview	Updated (UTC)
posthog-js	✅ Ready (Inspect)	Visit Preview	Nov 20, 2024 8:20am

[github-actions]

Size Change: +16.6 kB (+0.53%)

Total Size: 3.14 MB

Filename	Size	Change
dist/all-external-dependencies.js	206 kB	+1.44 kB (+0.7%)
dist/array.full.js	358 kB	+1.24 kB (+0.35%)
dist/array.full.no-external.js	357 kB	+1.21 kB (+0.34%)
dist/array.js	172 kB	+907 B (+0.53%)
dist/array.no-external.js	171 kB	+816 B (+0.48%)
dist/dead-clicks-autocapture.js	14.3 kB	+699 B (+5.12%)	🔍
dist/exception-autocapture.js	9.36 kB	+657 B (+7.55%)	🔍
dist/external-scripts-loader.js	2.29 kB	+22 B (+0.97%)
dist/main.js	173 kB	+923 B (+0.54%)
dist/module.full.js	358 kB	+1.24 kB (+0.35%)
dist/module.full.no-external.js	357 kB	+1.21 kB (+0.34%)
dist/module.js	172 kB	+1 kB (+0.59%)
dist/module.no-external.js	171 kB	+836 B (+0.49%)
dist/recorder-v2.js	115 kB	+1.06 kB (+0.94%)
dist/recorder.js	115 kB	+1.06 kB (+0.94%)
dist/surveys-preview.js	57.6 kB	+907 B (+1.6%)
dist/surveys.js	63.2 kB	+1.02 kB (+1.64%)
dist/tracing-headers.js	1.75 kB	+348 B (+24.8%)	🚨
dist/web-vitals.js	10.3 kB	-8 B (-0.08%)

ℹ️ View Unchanged

Filename	Size
dist/array.full.es5.js	254 kB

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[marandaneto]

low context n. N :D