chore: [SDK-5346] raise Mac Catalyst deployment target to 15

[nan-li]

Description

One Line Summary

Raise the SDK's Mac Catalyst deployment target from 14 to 15. SDK-5346.

Details

Motivation

Xcode 27 only accepts macOS deployment targets of 12.0 and up. The Catalyst floor of 14 maps to macOS 11.0, so every framework target fails to build for Mac Catalyst on Xcode 27. Catalyst 15 maps to macOS 12.0 and matches the iOS floor from #1749.

Scope

• The SDK project no longer sets a separate Catalyst deployment target, so Catalyst builds follow the iOS target of 15.
• Package.swift declares Mac Catalyst 15. Catalyst apps on macOS 11 can no longer use the SDK.
• Both podspecs drop their Catalyst 14 override. CocoaPods already set the pod target to 15.0 from s.platform, so the override never applied.
• The CI Catalyst job compiles its host for Catalyst 15.

Testing

Unit testing

No test changes.

Manual testing

Built OneSignalFramework, OneSignalInAppMessages, OneSignalLocation, OneSignalLiveActivities and OneSignalExtension for Mac Catalyst on Xcode 27.0 with no errors. The built frameworks report a Catalyst minimum of 15.0 and a macOS minimum of 12.0. Compiled and ran the CI Catalyst host against them at 15.0 with no warnings. Built a CocoaPods app that uses OneSignalXCFramework from this branch for Mac Catalyst on Xcode 27.0, before and after the podspec change. The pod target resolves to Catalyst 15.0 both times and the app builds.

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

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