Move start call of unused services off the main thread

[jinliu9508]

Description

One Line Summary

Move start call of unused services off the main thread to make the initWithContext more efficient.

Details

Motivation

Our SDK initialization is currently taking longer to finish compare to some other SDKs. One of the reason is we construct service components like Location Manager or IAM Manager during the initialization phrase when they are not really needed until later. This PR aims to move the initialization of these services to background thread so they don't slow down the overall SDK initialization.

Scope

The retrieval of services that were changed to initialize in background is not longer from a saved instance in OneSignalImp.kt. Instead, each of these components has a getter that retrieve its instance from the service provider.

Testing

Manual testing

• I measure how long the initialization takes by tracking the start and finish time when 'initWithContext' is called. In my testing in a pixel 3a API 34 emulator, it took an average of 600 ms to complete initialization before the change and around 300 ms after the change, which is around ~50% faster.
• Send notification, add tags, and outcome work.
• Calling 'initWithContext' in a background thread works. Other OneSignal calls can only work if they are called after 'initWithContext' and in the same thread.

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
  • If it is hard to explain how any codes changes are related to each other then it most likely needs to be more than one PR
• 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.
  • Simplify with less code, followed by splitting up code into well named functions and variables, followed by adding comments to the code.
• I have reviewed this PR myself, ensuring it meets each checklist item
  • WIP (Work In Progress) is ok, but explain what is still in progress and what you would like feedback on. Start the PR title with "WIP" to indicate this.

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This change is 

[jkasten2]

Left another 2 comments.

Also this existing comment is still unanswered and not addressed:
https://github.com/OneSignal/OneSignal-Android-SDK/pull/2127/files#r1644805601

[jkasten2]

Tests are failing on CI, made a comment about one test that will not pass often.

[jkasten2]

Changes look good now, but probably want to rebase to clean up a few a few of the fixup commits.