[ModulesGraph] Avoid re-fetching and sorting packages multiple times

`load` builds a list of packages in topological order already
and that's exactly what ModulesGraph wants, let's pass resolved
packages to it directly instead of having to re-build the list.

Author: xedin

Sources/PackageGraph/ModulesGraph+Loading.swift

@@ -100,8 +100,6 @@ extension ModulesGraph {
                 flattenedManifests[node.identity] = node
             }
         }
-        // sort by identity
-        allNodes = flattenedManifests.keys.sorted().map { flattenedManifests[$0]! } // force unwrap fine since we are iterating on keys
 
         // Create the packages.
         var manifestToPackage: [Manifest: Package] = [:]
@@ -169,6 +167,7 @@ extension ModulesGraph {
         return try ModulesGraph(
             rootPackages: rootPackages,
             rootDependencies: resolvedPackages.filter { rootDependencies.contains($0.manifest) },
+            packages: resolvedPackages,
             dependencies: requiredDependencies,
             binaryArtifacts: binaryArtifacts
         )

Sources/PackageGraph/ModulesGraph.swift

@@ -162,14 +162,15 @@ public struct ModulesGraph {
     public init(
         rootPackages: [ResolvedPackage],
         rootDependencies: [ResolvedPackage] = [],
+        packages: [ResolvedPackage],
         dependencies requiredDependencies: [PackageReference],
         binaryArtifacts: [PackageIdentity: [String: BinaryArtifact]]
     ) throws {
         let rootPackages = IdentifiableSet(rootPackages)
         self.requiredDependencies = requiredDependencies
         self.inputPackages = rootPackages + rootDependencies
         self.binaryArtifacts = binaryArtifacts
-        self.packages = try topologicalSort(inputPackages, successors: { $0.dependencies })
+        self.packages = packages
         let identitiesToPackages = self.packages.spm_createDictionary { ($0.identity, $0) }
 
         // Create a mapping from targets to the packages that define them.  Here