Move PackageCollectionsProtocol to async/await

[AndrewHoos]

Move PackageCollectionsProtocol to async/await

Motivation:

async/await is easier to read and reason about then the callback APIs

Modifications:

PackageCollectionsProtocol is now expressed in terms of async methods instead of callbacks
callback to async bridge methods are removed
Replaced usage of DispatchGroup with async let
PackageMetadata init has default values for optional and array values

Result:

More readable code

[MaxDesiatov]

@swift-ci test

[rauhul]

❤️ negative diff PRs

[MaxDesiatov]

Thank you so much! 😊

[AndrewHoos]

/home/build-user/swiftpm/Sources/PackageCollections/PackageCollections.swift:343:22: error: cannot find 'withCheckedContinuation' in scope
341 |         let packageSearchResult = try await self.findPackage(identity: identity, location: location, collections: collections)
342 |         // then try to get more metadata from provider (optional)
343 |         return await withCheckedContinuation { continuation in
    |                      `- error: cannot find 'withCheckedContinuation' in scope
344 |             self.metadataProvider.get(identity: packageSearchResult.package.identity, location: packageSearchResult.package.location) { result, provider in
345 |                 switch result {

[AndrewHoos]

Something odd with importing _Concurrency seems to break on Linux?

[MaxDesiatov]

import _Concurrency is required when building with CMake.

[MaxDesiatov]

@swift-ci test

[MaxDesiatov]

@swift-ci test windows

[MaxDesiatov]

@ahoppen could the macOS failure be related to recent SourceKit-LSP changes?

error: value of type 'SourceKitLSPOptions' has no member 'swiftSDK'

[AndrewHoos]

@swift-ci test