Set ConfigureAwait(bool) on IAsyncEnumerators in await foreach loops

[ScottRosenberg2]

Describe the problem you are trying to solve

Currently CA2007 requires ConfigureAwait(bool) to be set on all instances of awaiting a task.
It does not currently catch cases where you have awaited an IAsyncEnumerator in an await foreach loop.
If you write:
await foreach (var x in someIAsyncEnumerator) { }
I'd like to see it suggest:
await foreach (var x in someIAsyncEnumerator.ConfigureAwait(someBool)) { }

Currently: It does not recognize missing ConfigureAwait on IAsyncEnumerators

Describe suggestions on how to achieve the rule

Create a rule similar to CA2007, or modify CA2007 to correctly identify await foreach IAsyncEnumerators

Additional context

Not having this rule lead to having deadlocks in our code, until manually fixed.

[mavasani]

Create a rule similar to CA2007, or modify CA2007 to correctly identify await foreach IAsyncEnumerators

@buyaa-n @jeffhandley @stephentoub

[stephentoub]

I think we should just update CA2007 for this. It's the same case, it's just that the underlying awaits are hidden behind code gen and so you need to lift the ConfigureAwait to be specified in a different location.