Resolve coroutines compilation warnings

Description

This MR has three separate components:

1. The removal of existing coroutine annotations within the codebase
2. The addition of opt-in annotations when obsolete/experimental functions are first invoked
3. The inclusion of a compiler flag to allow for the use of the opt-in annotations

For more details see note in !1336 (merged).

Motivation and Context

The objective of this change is to address the large number of warnings being propagated throughout the codebase due to the coroutines API. Prior to this change, a total of 1,532 compilation warnings were reported. Following the change 708 warnings were reported (53.78% decrease). The significant reduction in warnings will allow the development team to more easily address the remaining issues.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have read the CONTRIBUTING section of the README document.