feat: Update support for segment analytics

[benjackwhite]

Changes

Fixes #1106

Annoyingly Segment's documentation does not match reality. They claim that the Analytics JS will always have non-promise responses once it is ready but this isn't the case.

• Changes the Segment setup to all happen in one function
• Accounts for the User object being a promise or not
• Handles both distinct_id and device_id

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!)

[github-actions]

Size Change: +1.54 kB (0%)

Total Size: 962 kB

Filename	Size	Change
dist/array.full.js	230 kB	+392 B (0%)
dist/array.js	127 kB	+383 B (0%)
dist/es.js	128 kB	+383 B (0%)
dist/module.js	128 kB	+383 B (0%)

ℹ️ View Unchanged

Filename	Size
dist/exception-autocapture.js	12.2 kB
dist/recorder-v2.js	108 kB
dist/recorder.js	108 kB
dist/surveys-module-previews.js	62 kB
dist/surveys.js	58.3 kB

_{compressed-size-action}

[pauldambra]

🚢

[robbie-c]

LGTM

edit: lol too slow

[kamui]

Thank you!