[iOS/macOS] Rename onboarding shared pixel params and bucket daysSinceInstall

[rachelmcr]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1202818073656551/task/1217051716311541?focus=true
Tech Design URL:
CC:

Description

Updates the onboarding shared pixel parameters as agreed in New parameter names and buckets:

• Uses more transparent parameter names: event, installType, daysSinceInstall
• Buckets the daysSinceInstall values, no longer dropping values over 28 (instead using a 28+ bucket)

Testing Steps

1. Build and run the macOS app.
2. Debug → Reset Data → Reset Onboarding
3. Close the window and reopen it.
4. Confirm m_mac_onboarding_welcome is shown with parameters event, installType, daysSinceInstall (no parameters e, it, d).
5. Confirm daysSinceInstall uses a bucket value corresponding to the days since the app was originally installed (e.g. 0, 1-3, 28+).

Impact

None: Internal tooling

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Internal references:

Definition of Done | Engineering Expectations | Tech Design Template

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Note

Low Risk
Analytics-only pixel parameter changes with no user-facing behavior; downstream dashboards must expect new keys and bucket values instead of legacy e/it/d.

Overview
Aligns onboarding shared pixels on iOS and macOS with clearer parameter names and bucketed install-age reporting.

Parameter renames on fired pixels: e → event, it → installType, d → daysSinceInstall. The handler and OnboardingSharedPixelEvent parameters map, plus iOS/macOS params_dictionary.json5, are updated together.

daysSinceInstall is no longer a raw day count capped at 28 (older installs omitted the param). It now sends string buckets: 0, 1-3, 4-10, 11-28, and 28+ for 29+ days. Tests cover each bucket and the negative-day omission case.

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[rachelmcr]

Note: We shouldn't merge this until the pipeline is updated to accommodate the changes: https://app.asana.com/1/137249556945/project/1108686900785972/task/1216871249295897?focus=true