Review Acceptance Modifications to SE-0303 (Package Manager Extensible Build Tools) (#1441)
Review Acceptance Modifications to SE-0303 (Package Manager Extensible Build Tools) (#1441)

* [SE-0303] Acceptance modification: Mark the plugin entry point with `async` so that it is allowed to call other async APIs.

* [SE-0303] Acceptance modification: Add an explicit Severity declaration and an `emit(_ severity, `... function based on review feedback.

Also add the missing documentation and the mistake of leaving out `#file` and `#line` from the proposal (this was their stated purpose in the proposal).
natecook1000/swift-evolution,apple/swift-evolution,abertelrud/swift-evolution,abertelrud/swift-evolution,apple/swift-evolution,natecook1000/swift-evolution