Implement deterministic collapse of 'await' in 'await using'

[Ron Buckton (rbuckton)]

This updates the __disposeResources helper to align with a recent change to the DisposeResources algorithm that reached consensus in the June TC39 meeting. It has the effect of reducing extraneous Await operations for cases like the following:

{await using x=null,y=null,z=null;HAPPENS_BEFORE();}HAPPENS_AFTER();

It is a requirement that an await using declaration must trigger an Await when exiting the block such that HAPPENS_BEFORE() and HAPPENS_AFTER() occur in different turns, even if the resource recorded was null/undefined. Prior to this change, the DisposeResources algorithm would Await for each null/undefined in an await using, which could introduce significant delays to function execution. Rather than Await-ing three times in the above example, we can collapse these down to a single Await instead to preserve the aforementioned requirement.

I should note that our downlevel emit is not as efficient as a native implementation since we must await the result of __disposeResources, which introduces 1-2 turn overhead as it adopts the state of the resulting Promise. The only way we could make that more efficient would be to inline the behavior __disposeResources into the finally block, which would dramatically increase emit size.

For more context as to the effects of the DisposeResources algorithm as a result of this change, see tc39/proposal-explicit-resource-management#219 (comment)

As this changes our helpers, you can find a companion PR for tslib here: microsoft/tslib#262

Fixes#58876