RUM-4829 Upgrade CI stack to Xcode 15

[ncreated]

What and why?

📦 This PR updates the repo so we can run Xcode 15 on CI.

It follows earlier #1891 where we dropped iOS and tvOS 11.0 deployment targets (no longer available in Xcode 15).

How?

3 main changes:

• Aligned Swift version to 5.9 which comes with Xcode 15.0. To make this configuration central, I removed all Xcode project overrides and defined it in Base.xcconfig (following the pattern from RUM-4829 Bump iOS and tvOS deployment target to 12.0 #1891). Package.swift and CP podspecs are updated accordingly.
• Re-generated SR snapshot using iPhone 15 Simulator and iOS 17.5. New snapshots can be seen in https://github.com/DataDog/dd-mobile-session-replay-snapshots/commit/5d8f4ffffabaa507dadc07bd89498bb962a64853 (internal). I did it a deeper look using diffusion diffs to make sure there is no visible regression.
• Default CI stack will be changed to Xcode 15. This will happen before merge.

Testing:

• I ran each stage (unit tests, SR snapshots, integration tests, smoke tests, tools) in isolation using temporary Xcode 15 stack. All worked fine ✅ ✅ ✅ ✅ ✅.
• I don't expect any impact on release automation because smoke tests for all dependency managers worked fine (including XCFrameworks build).

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes

Custom CI job configuration (optional)

• Run unit tests for Core, RUM, Trace, Logs, CR and WVT
• Run unit tests for Session Replay
• Run integration tests
• Run smoke tests
• Run tests for tools/

[datadog-datadog-prod-us1]

Datadog Report

Branch report: ncreated/RUM-4829/upgrade-ci-to-xcode15
Commit report: 39fe41d
Test service: dd-sdk-ios

✅ 0 Failed, 3303 Passed, 0 Skipped, 3m 6.86s Total Time

[mariedm]

🙌🚀

[ganeshnj]

What is the minimum version of the iOS simulator we are testing on in CI?

[ganeshnj]

nice

[ganeshnj]

nice

[ncreated]

What is the minimum version of the iOS simulator we are testing on in CI?

@ganeshnj we use iPhone 11,OS=latest (see in Bitrise.yml). Effectively it means iOS 17.5 for the current stack. We can look into distinguishing "high" and "low" simulators once we move to GitLab.