Fix compiler references when building inside VS

If for a source project a contract project exists, then the contract project's TargetPath should be passed to the compiler. This is handled by the SDK by default when `ProduceReferenceAssembly` is true. As dotnet/runtime doesn't use the `ProduceReferenceAssembly` feature yet, a custom target adds the necessary `ReferenceAssembly` metadata to the `TargetPathWithTargetPlatformMoniker` item which then is transformed to references for the compiler. That works fine on the CLI as the `GetTargetPathWithTargetPlatformMoniker` target runs after the ProjectReference to the ContractProject is resolved and its target path is available.
Inside VS the target ordering is different and the `ResolvedMatchingContract` item was empty as the ProjectReference to the contract wasn't yet resolved. The fix for that is to add a dependency onto the `ResolveProjectReferences` target to guarantee that the `ResolvedMatchingContract` item is populated in time.

Noticed this when the build of System.ComponentModel.Composition.Registration failed because the implementation assembly of System.ComponentModel.Composition was passed to the compiler instead of the reference assembly.

eng/resolveContract.targets

@@ -25,6 +25,7 @@
   <!-- Allow P2Ps that target a source project to build against the corresponding ref project. -->
   <Target Name="AnnotateTargetPathWithTargetPlatformMonikerWithReferenceAssembly"
           Condition="'$(HasMatchingContract)' == 'true'"
+          DependsOnTargets="ResolveProjectReferences"
           AfterTargets="GetTargetPathWithTargetPlatformMoniker">
     <ItemGroup>
       <TargetPathWithTargetPlatformMoniker ReferenceAssembly="@(ResolvedMatchingContract)" />