fix: [SDK-4927] migrate to Unity External Dependency Manager

[fadi-george]

Description

One Line Summary

Replace the deprecated bundled Google EDM4U integration with Unity External Dependency Manager 2.0.

Details

Motivation

Unity Asset Store rejected the v6 submission because it referenced Google's superseded EDM4U package. Unity now requires package maintainers to use com.unity.external-dependency-manager. See Unity’s EDM setup guidance.

Scope

• Declare Unity EDM 2.0 in the Android and iOS UPM packages.
• Remove the legacy EDM4U installer and vendored demo binaries.
• Refresh demo lockfiles, project settings, notices, and documentation.
• Add distribution checks preventing legacy EDM4U from being reintroduced.
• No public OneSignal API changes.

Testing

Unit testing

No unit tests were added because this changes Unity package resolution and distribution metadata rather than runtime behavior.

Manual testing

• Ran python3 .github/scripts/validate-unity-distribution.py.
• Ran npm pack --dry-run for all three UPM packages.
• Resolved Unity EDM 2.0 and compiled the demo projects with Unity 2022.3 and Unity 6.

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
• I have reviewed this PR myself, ensuring it meets each checklist item

[cursor]

Adversarial review (high / medium)

High — Legacy Google EDM left in customer projects
Removing InstallEdm4uStep and the reset cleanup of Assets/ExternalDependencyManager leaves upgrades with no migration for existing Assets-folder EDM4U. Dual resolvers commonly break Android/iOS resolution; Unity EDM 2.0 docs recommend keeping only one manager active and deleting Assets installs. Add a setup step and/or v6 migration note to detect and remove/disable legacy Google EDM.

Medium — demo-no-location under-validated
CI blocks legacy EDM in both demos, but validate_packages() only checks examples/demo/Packages/manifest.json. Mirror those manifest checks for demo-no-location.

Medium — Demo EDM settings asymmetry
examples/demo commits ExternalDependencyManagerSettings.json (edmEnabled: true); demo-no-location gitignores most ProjectSettings/, so it does not. Track the same settings (or document why not) to avoid prompt/resolution drift.