Figure out whether project system should be using ConfigureAwait(true/false) on its await calls

_From @davkean on November 13, 2015 20:51_

We've currently suppress all usages of RS0003 in the project system code:

```
Warning RS0003  Do not directly await a Task without calling ConfigureAwait
```

We should review all instances of the suppressed values and figure out if we want `ConfigureAwait(true)` or `ConfigureAwait(false)`.

_Copied from original issue: dotnet/roslyn#6770_
