DesignTime builds are slow in VS with the latest MSBuild targets.

[jlaanstra]

Design-time builds in VS seems to be taking quite a bit of time, slowing down branch changes, project reloads etc.

Especially ResolveAssemblyReferencesDesignTime and ResolveProjectReferencesDesignTime seem to suffer from this.

[jlaanstra]

@Scottj1s Looks like this is caused by the fact that VS runs ResolveProjectReferences on project load. That in turn calls GetTargetPath on each project reference.

We hook into GetTargetPath to return info regarding the C++/WinRT generated winmd and to do so we currently resolve that project's project references, which essentially traverse the whole tree of project references. Since VS runs this for each project, this essentially creates an O(n^2) amount of project reference evaluations which can add up and significantly affects project load in larger solutions.

CX solves this by having the Link.GenerateWindowsMetadata set to true.
C# solves this using WinMDObj

I propose we add a similar property to C++/WinRT, that indicates that this project output is a C++/WinRT generated winmd. The project templates would set that to true by default.

Thoughts?