fix: Make selectPlacement Use Message Queue

[BrandonStalnaker]

Summary

• Timing issues led to user attributes not being set when an identify needed called within the selectPlacements method. Changing the dispatch to the message queue guarantees that all the setUserAttributes are completed before the kit code is called and thankfully in 'attemptToLogEventToKit' of 'MPKitContainer.mm' (which comes after that dispatch in the mp core code) we dispatch back to the main queue as needed.

The change to 'MPKitContainer.mm' is just to make debugging with breakpoints easier.

Testing Plan

• Was this tested locally? If not, explain why.
• Tested with example app on simulator

Reference Issue (For mParticle employees only. Ignore if you are an outside contributor)

• Closes https://go.mparticle.com/work/REPLACEME

[mparticle-automation]

🎉 This PR is included in version 8.34.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀